[Aptitude] Product Consistency: If Sugar price increases then consumption should be Decreased by What %, Time-Speed-Distance problems, shortcuts for SSC, IBPS, CSAT, CAT

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IAS Mock Interviews
  1. Case: Sugar Consumption Budget don’t change
  2. Case: Salary comparison: How much more or less?
  3. Case: Increased consumption absolute value
  4. Case: Apples price decrease absolute value
  5. Case: Time-Speed-Distance
  6. Mock questions
  7. Food for thought
IF you want to master this method, then don’t just read the article, simultaneously do all calculations in your rough-note/paper.

Case: Sugar Consumption Budget don’t change

Q. if price of sugar is increased by 25%. But a family wants to keep its expenditure same as earlier. Then they should decrease their consumption by how much percentage?

  • Suppose initial price of Sugar was Rs.100 per kg
  • And this family needs 2 kg per month. (=quantity consumed)
  • So what is their budget (or Expenditure?)
Before price rise
Price100
Quantity2 kg
Budget = Price x quantity100 x 2=Rs.200 per month

Now the price of sugar is increased by 25%.
So if previously it was Rs.100 per kg, now it is Rs.100+25=Rs.125 per kg.

BeforeAfter
Price100125
Quantity2 kg
Budget = Price x quantity100 x 2=Rs.200 per month

If the family still wants to buy 2 kg sugar, they’ll have to pay Rs.125 x 2 = Rs.250. But they don’t want to increase their budget (Expenditure). Obviously they will have to cut down on their monthly consumption (Quantity of sugar.)
To solve this problem, just take ratio of both prices
100/125
=(25×4)/(25×5)
=4 / 5
It means 100/125=4/5
Now, reverse this ratio (4/5 =>5/4) and write it, in the table.
Means, in 100’s column, I’ll write 5 and in 125’s column, I’ll write 4.

BeforeAfter
Price100125
Ratio reversed?54
Demand2 kg
Budget = Price x Demand100 x 2=Rs.200 per month

What is the percentage change in Ratio-Reversed?
Well, before it was “5” and after it has decreased to “4”.
% decrease from 5 to 4 is
=(5-4)/5
=1/5
=20% decrease.
That’s our answer.
If price is increased by 25% then we must decrease our consumption by 20% to keep the budget same.
Let’s check if our approach is correct.
According to above technique, we’ve found that consumption /demand should decrease by 20%.
So if earlier family consumed 2kg
Now they should consume only 100% minus 20%=80% of original demand
=80% of 2kg
=0.8 x 2
=1.6 kg

Update the table.

BeforeAfter
Price100125
Quantity54
Budget = Price x quantity2 kg1.6
Price100 x 2=Rs.200 per month125 x 1.6=Rs.200 per month
  • As you can see, if we decrease demand/consumption from 2 kg to 1.6 then budget remains same (Rs.200).
  • It proves that we’ve not made any mistake.

Another way is to use readymade formula

Formula

Percentage decrease = 100m / (100+m), where m is the original percentage.
Therefore
Percentage decrease in sugar case
=100 x 25 / (100+25)
=100 x 25/125
=20% decrease.

  • You can use whichever technique you like.
  • But once you master product consistency, lot of profit-loss, time-speed-distance questions can be solved in less than a minute.
  • Anyways, lets try some more “easy” questions and then move to difficult ones.

Case: Salary comparison: How much more or less?

  1. If Salary of Mr.Abdul is 25% more then Mr.Bhide, then Mr.Bhide’s salary is how much % less than Mr.Abdul’s?

Assume Bhide earn Rs.100 per month Then Abdul has to earn Rs.100+25=125
Fill up the table.

BhideAbdul
Salary100125
Ratio (reversed)

Now get the ratio
100/125=4/5
Reverse it (from 4/5 to 5/4) and plug it in the table

BhideAbdul
Salary100125
Ratio (reversed)54

That’s it. What is the decrease?
(5-4)/5 x 100
=1/5 x 100
=20% less
Final answer: Mr.Bhide’s salary is 20% less than Abdul’s.
Ofcourse you could directly calculate: (125-100)/125=20% but that won’t help us quickly solve the ‘complex’ cases situation like following.

Case: Increased consumption absolute value

Q. A family spends Rs.600 on sugar every month. The price of sugar is decreased by 20% and they’re able to buy 5kg sugar more. What was the original price of sugar (per kg)?

  • This is not at all complicated. Budget =Rs.600 (Constant)
  • Assume that original price is Rs.100 (please note: this is not the answer, we are just ‘assuming).
  • New price is 20% less = 100 minus 20 = Rs.80 per kg
  • Assume that originally they used to buy “m” kilos of sugar every month.
BeforeAfter
PriceRs.100Rs.80
Ratio-reversed
QuantityM
Budget600600

So if price is decreased by 20% then consumption quantity should increase by what percentage?
Just take ratio of price
100/80
=10/8
=5/4
Reverse It and fill up in the table

BeforeAfter
PriceRs.100Rs.80
Ratio-reversed45
Quantitym
Budget

So what’s the increase in quantity ?
Just look at the ratio reversed: 4 to 5. So increase is:
(5-4)/4 x 100
=1/4 x 100
=25%

  • It means if sugar price decreases by 20% then we can buy 25% more sugar.
  • So if earlier this family used to by “m” kilos of sugar, now they should be able to buy Total= (m + 25% of m) kilos of sugar.

How much more sugar can they buy? 25% of m
But the question itself says that family is able to buy 5 kg sugar more.
It means
25% of m =5 kg
(25/100) x m=5
M=5 x (100/25)
M=20kg

Another way is (% to fraction)

25% when converted to fraction =1/4
So 1/4th of m=5 kg
So m= 5 x 4=20 kg.
In either way: it means originally family used to buy 20 kilos of sugar.
And their budget was Rs.600. (given in the question)
So what was the per kilo price of sugar?
20kg=Rs.600
So 1 kg=600/20=30Rs. per kilo
Final answer= original price of sugar was Rs.30 per kg.
Let’s try a similar question, so our concept is crystal clear.

Case: Apples price decrease absolute value

This is also from SSC-CGL exam.
Q. A man spends Rs.54 on apples every month. Price of Apple is decreased by 20% and this man can buy 10 apples more. What is the reduced price per dozen?
If price is 20% decreased => consumption should increased by 25% (as seen in previous case)
Suppose he used to buy “m” number of apples initially.
Now he can by 25% more apples.
But question itself says that he is buying 10 more apples.
Therefore,
25% of m =10
1/4 of m=10 (because 25%=25/100=1/4)
1/4 of m =10
M=40

So what was the original price?

Total 54 rupees spent on 40 apples
=Rs.54/40
And we’ve to find answer in “dozen” so multiply with 12
Original price= Rs.(54/40) x 12
Donot simplify yet.
We’ve to find reduced price.
Question says, price is reduced by 20%.
So new price
=100 Minus 20=80%of original price
=0.8 x (54/40) x 12
=Rs.12.96
Final answer: the reduced price of apples is Rs.12.96 per dozen.

Another approach

Originally he bought 40 apples.
Now he can buy 25% more
=100+25=125% of original apples
=1.25 x 40
=50 apples.
And his budget is Rs.54 means he buys 50 apples for 54 rupees,

50 apples= 54 rupees
12 apples= how much?

How much = 54 x 12 / 50 =Rs.12.96 per dozen.
Now let’s apply this concept in Time-Speed-Distance question

Case: Time-Speed-Distance

Again from old SSC-CGL exam
Q. Walking at 6/7th of his usual speed, a man is 25 minutes late for his destination.
What is his usual time to cover this distance (in hours)?
Speed x time = distance
This is same as price x quantity = budget.
Here distance remains the same, just like in “sugar-cases”, budget remains the same.
We don’t know his speed, so let’s assume his usual speed = 1 kmph
And his late speed = 6/7th of usual speed = 6/7 x 1= 6/7 kmph

Usual caseLate case
Speed16/7
Ratio reversed

Just take ratio
Usual/late=1/(6/7)=7/6
Reverse it (7/6 to 6/7 )and put it back in the table.

Usual caseLate case
Speed16/7
Ratio reversed67
Time“T”

Ok so if speed is decreased to 6/7th then time is increased by what fraction (or percentage?)
6 to 7
=(7-6)/6
=1/6 increase in time.
Suppose his usual time was “T”, then it should be increased by 1/6th of original time “T”
But we know that he is late by 25 minutes.
It means 1/6th of T=25 minutes
1/6 x T = 25
T=25 x 6=150 minutes
But the question is asking time in hours.
150 minutes
=60 minutes + 60 minutes + 30 minutes
=1hour + 1 hour + 30 minutes
=2 hours and 30 minutes
Another way to convert minutes into hours
60 minutes = 1 hr
150 minutes = how many hours?
Therefore: How many hours = 1 x 150 / 60
When you divide 150 by “60” you 2 as quotient and 30 as remainder. So Correct answer is 2 hours and 30 minutes.
Important: In Minutes to hour conversion via division method, You should not cut zeros, else you get wrong answer.
For example, 150/60= 15/6 but when you divide 15 by 6, you get remainder 3 = answer comes as 2 hours and 3 minutes = wrong answer.

Mock questions

  1. Journalist Popatlal’s income is 37.5% less than Dr. Iyyer’s. Then Dr.Iyyer’s income is how much % more than Popatlal’s income?
  2. If price of Desi-liquor is increased by 20% then Mohan should cut down consumption by what %, to keep his budget unchanged?
  3. Petrol price is doubled. But we don’t want to raise our expenditure. Then We should cut down our petrol consumption by what percentage?
  4. If the speed of a motorboat is decreased by one fourth, then journey completion time should increase by what percentage?
  5. Price of rice is increased from Rs. 6 to 7.5 per kg. If we don’t want to increase our Expenditure. We should decrease our rice-consumption by what percentage?
  6. Mobile company increased the call charges by 50%. If I want to keep my budget unchanged, I should reduce talk-time by what percentage?
  7. Dish TV has reduced the channel prices by 20% now I’m able to subscribe to 5 more channels in the same budget of Rs.400. How many channels did I subscribe earlier?
  8. Writing at 3/4th of my usual speed, I finished the question paper 20 minutes late. Had I written the answers at my regular speed, I could have finished the whole paper in how many hours?
  9. Earlier UPSC used to ask 579 questions for 2900 marks. Now they want to decrease number of questions by 20% but want to keep total marks same as earlier. So, they should increase the marks per question by what percentage?
  10. If a politician’s bribe income is decreased by 10% then his anger increases by how much percentage? hahaha

Answers

  1. Iyyer Popat
60% Perhaps this is the reason why Popat is unable to find a bride while Iyyer walked away with Babita-ji.
  1. Desi liquor
16.67% decrease (1/6)
  1. Petrol Double
50% decrease in consumption.(hint double = 100 to 200 =100% increase)
  1. Motorboat
One fourth=25% decrease=> 33.33% increase in time.
  1. Rice
25% increase in price =>20% reduction in consumption.
  1. Mobile talktime
50% increase in call rates=>33.33% decrease in talktime to keep budget unchanged.
  1. Dish TV
Earlier I had subscribed to 20 channels. 20% decrease in price= 25% increase in number of channels. so 1/4 of original channels=5, hence original number of channels=5 x 4 =20.
  1. Writing speed
3/4 th of writing speed= reverse ratio is 4:3; and increase in time is 1/3 (=33.33%). So if 1/3 rd of original time= 20 minutes late.
Then original time = 20 x 3 =60 minutes = 1 hour.
  1. Anger
11.11% increase in anger lolz
  1. UPSC
Absolute values 579 and 2900 are irrelevant! No need to waste time in dividing them. 20% decrease=> increase marks per question by 25% percentage.

Food for thought

Try these two questions: (You can solve them via STD table method but try to solve them via this product consistency method. You’ll get the answer much more quickly!)

  1. Jethalal goes to shop at the speed 30 km/h, and he reaches six minutes early. Next day he goes at the speed of 24 km/h, and he reaches five minutes late. Find the distance between his home and shop. (Ans=22kms)
  2. Tappu walks from home to school @5kmph and reaches 15 minutes early. After the school is over, he is very tired. So he walks back from school to home at a slow speed of just 3kmph and reaches 9 minutes late. Find distance between his home and school. (Ans=3 kms)

But How to apply “product consistency” ^here in these two question? =will be explained later.
All [Aptitude] Articles are listed at Mrunal.org/aptitude

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83 Comments on “[Aptitude] Product Consistency: If Sugar price increases then consumption should be Decreased by What %, Time-Speed-Distance problems, shortcuts for SSC, IBPS, CSAT, CAT”

  1. its simple formula is (a/100-a) where ‘a’ is the 37.5% decrease of salary.

  2. Hello sir /madam
    can we solve following kind of ques by RR technique:
    A has emplyed a worker for a certain work. He pays rs.20/- for each working day and payment is reduced by rs.3/- for each non working day of worker.
    For how many worker remain absent from work if at the end of 120 days, worker gets rs.560/- as total remuneration?
    kindly help. Thanks in advance

    1. i made this equation for this question-
      20d-3(120-d)=560 where d is the no of working days
      solving this we get the answer as 80 days he did not work.

  3. PRINTING MISTAKE =
    9 IS 10
    10 IS 9

  4. sir, please say the detail answer of these question.

    1)The price of an article first increased by 10%, then decreased by 20% and then increased by 30%. If the final price is Rs. 3432, what was the original price?

    1.Rs. 2500
    2.Rs. 3000
    3.Rs. 2000
    4.Rs. 3500
    5.Rs. 1500
    2)In how many ways 5 prizes can be distributed among 3 students if one student can get any number of prizes?

    1.10
    2.21
    3.24
    4.12
    5.22
    3) Four persons are there in a function and six seats are vacant. In how many ways they can be seated?

    1.220
    2.330
    3.360
    4.120
    5.480
    4)A bag contains six black balls, 4 green balls and 3 red balls. If 3 balls are picked at random what is the probability that they are of same colour?

    1.25/286
    2.25/216
    3.42/72
    4.3/13
    5.4/13

    1. 1) 3000
      2) 12
      3) 360
      4) 25/286

  5. sir i am not finding percentage concept from starting..plzz send me a link

  6. explain food for thought second question

  7. Harish sold two chairs at Rs 600. In one he gain 20% & on the other he loses 20%. Find the gain & loss percent in whole transaction…..

    1. 400/100 i.e. 4% loss …. simlpy X to the power 2 divided by 100 always results in loss when selling price is same and % profit and loss is also same.

  8. Percentage decrease = 100m / (100+m), where m is the original percentage.
    Therefore
    Percentage decrease in sugar case
    =100 x 25 / (100+25)
    =100 x 25/125
    =20% decrease.
    How m=25 derive…! In here if m is original percentage then it must be100 not 25.. But it must be Inc. Or Dec. Value!! Please give some comment or guideline on this.

  9. The price of sugar is increased by 28%. Therefore a family reduces its consumption so that the increment in the expenditure of sugar is only 20%. If the consumption of sugar is 15 kg before the increment, what is the consumption now?

  10. Ans for 1st Ques:

    130 % of 80 % of 110 % of X =3432

    Then X=3000

  11. due to increase in the price of edible oil in the market by 25% the consumption of this oil in a family is decreased by 12 %.The expenditure of family is

  12. hii sir/mam
    Q all head is 71
    & all foot are 228
    then how many 4 foot animal

  13. short tricks of the ques “the smallest number added to 680621 to make the sum a perfect square is :?”

  14. If the price of a commodity is reduced by 10% . How much quantity can be bought with the same money which was sufficient to by 90 kg at t original price?

  15. If value of sugar increased by 20%. What % decrease its consumption that its expenditure only increased by 12%.

  16. the price of an article is increased by 12%,20%,and 25%.what is effective percentage increase in the price of the article.

  17. The empty weight of jar is 20.% of its weight when it is completely filled with water.if some water is taken out of jar such that the currnt weight of the jar is 40% of its weight when it is completely filled with water.what % of water is taken out of jar?
    1) 70% (2) 60% (3) 85% (4) 50% (5) none of these.
    plz help me to solve.

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