- [Block#2] %, STD and Stat
- Appendix Download link: Topic wise Sorted NCERTs
- In the previous article, we saw how to prepare number system, surds-indices, linear and quadratic equations for CDS maths paper. click me
- Now in this second article, we’ll see how to approach percentage, profit-loss, simple-compound interest rate, time-speed-distance-work and statistics-Data interpretation related problems.
- In the third article, we’ll see how to approach geometry, trigonometry and remaining misc. Topics. click me
|topics in this block||avg. MCQs in each of the last four CDS exams.||priority|
|Profit loss, SI-CI, ratio-proportion||5||medium*|
|Time Speed Distance Work||7||high|
|statistics and Data interpretation||6||high|
*medium priority because in last two exams (of 2013), barely 3 and 2 MCQs respectively. The average is “5” only because in earlier times, they used to ask a lot from here. Still 2-3 MCQs are good because you hardly need to memorize any formulas.
Unlike the IBPS questions, here % or compound interest rate doesn’t require lengthy multiplication or division. Most of the time the numerators will be easily cut.
|7_8 Comparing Quantities||introduces to %, simple interest rates, profit||IAK|
|8_8 Comparing Quantities||compound interest rates||IAK*|
* IAK=”I already know”. Meaning you can ignore this chapter, if you’re basics are already good. (i.e. you’ve already cleared written stage of bank, SSC or LIC.)
You can even ignore above NCERTs, and directly use methods explained in following articles:
- Concepts of Marked Price and Successive Discounts (Profit-Loss) without (stupid) formulas
- Compound Interest Rate, Population Growth without Formulas
- Alligation: Advanced applications in Interest rates, Profit-loss, Average Wages (Wine-Water Concept) <=master this technique because often interest rate problems in CDS are based on this theme.
- Product Consistency: If Sugar price increases then consumption should be Decreased by What %, Time-Speed-Distance problems,
Then do Sarvesh Kumar’s chapters on: percentages, profit loss and discount, and CI/SI/installments. In each of them solve all illustrations/examples, introductory exercises and level1 exercises. you may ignore the ‘loan-installment’ related problems because I didn’t see them in last 5 years’ papers.
Demo MCQs from previous CDS Exam
SIMPLE INTEREST RATE
- A sum of money is lent on simple interest triples itself in 15 years and six months. In how many years will it be doubled?
- A men has invested Rs. 1000 on simple interest of certain rate, and Rs. 1500 at 2% higher rate. The total interest accumulated in three years is Rs. 390. What is the rate of interest for Rs. 1000?
- A man has borrowed Rs. 40,000 at 8% simple interest rate per and. At the end of second-year he has paid back certain amount, and at the end of fifth year, he gave Rs. 35,960 and cleared the debt. What is the amount did he pay back after the second year?
|COMPOUND INTEREST RATE||PROFIT-LOSS-MARKED PRICE & DISCOUNT|
Usually one or two MCQs from this portion each year. But still, the cost: benefit is great because no formulas to memorize.
|7_8 Comparing Quantities||basics of Ratios||IAK|
|8_13 Direct and Indirect Proportions||basics of variation||IAK|
- Since they’re not asking anything from definitions, you may directly goto Sarvesh Kumar chapter on Ratio proportion variations without touching NCERTs.
- Solve all the examples and questions upto level 1. (For rock solid grip, you may even do upto level II).
- also see this article: [Aptitude] Partnership and profit-sharing made Easy.
Demo MCQs from previous CDS exams
|RATIO: TWO ENTITIES||RATIO: THREE ENTITIES|
In this portion, NCERT not much useful because it runs on the LCM method and doesn’t dwell on all variety of questions, besides nothing asked from theory/definition.
TSDW is made up of two topics
- Time speed distance: related to cars, trains, platforms, boats etc.
- Time speed work: related to “A can complete a work in….”, “pipe A can fill the tank in …” etc.
All of these can be solved through just one formula: STD (speed x time =distance). Go through following articles:
Once you’ve got the idea of STD method, solve all the examples and questions given in Sarvesh Kumar’s book under the chapters:
- time and work (upto level 1)
- time speed and distance (upto level 1)
Then CDS MCQs will be a walk in the park.
TSD: Demo MCQs from Previous CDS Exams
|TRAINS, PLATFORMS, TWO MOVING ENTITIES||BOATS AND STREAMS|
|EARLY LATE||AVERAGE SPEED BASED|
TSW: Demo MCQs from previous CDS exam
|WAGE SHARING||EFFICIENCY RELATED|
|PIPES N CISTERNS||MULTIPLE MEN /WOMEN|
average 6MCQ per exam in last four exams from this section. But in the CDS maths paper, the statistics-DI portion differs from SSC-CGL / IBPS type exams because
- Theory / definition based MCQs asked.
- For data interpretation they don’t ask conventional pie-chart, bar-graph related cases. Instead they give frequency chart and you’ve to find mean / median / mode. (i.e. like the “stat” portion in the UPSC GS mains paper II under old syllabus.) Therefore you’ve to mugup those special formulas for continuous series etc.
first observe the MCQs
|Weighted average (wine-water)||AM (Arithmetic mean)|
|GM (Geometric Mean)||HM (Harmonic Mean)|
|find geometric mean of 125, 729, 1331||Consider these pairs: I (8,12); II (9, 11); III (6,24). Which of them have same harmonic mean?|
Now how to prepare? Go through following articles
|Weighted average (wine-water)||Arithmetic mean|
then Sarvesh Kumar chapter on Alligiation. (upto level1)
then Sarvesh Kumar chapter on Averages. (upto level1)
For geometric and harmonic mean
In the NCERT zip folder, I’ve included a word file giving the formulas and a few theory points. read it then pick a few random numbers and find their GM, HM on your own.
you’ll also find a few MCQs of GM, HM in Sarvesh Kumar’s chapter on “Sequence, series and progressions”.
First Observe the MCQs from past exams
Q1. Consider following data
IF THE arithmetic mean is 2.96, what is the missing frequency “A”? (options: 4/6/7/8)
Q2. Consider following data
|frequency||9||22||–||20||12||8||100 total frequency|
What is the modal class?
- 10.5 to 20.5 only
- 10.5-20.5 and 20.5-30.5
- 20.5-30.5 only
- there is modal class
Q3. for the following table, median is 14.4 and total frequency is 20.
Now answer the following two questions:
- What is the value of x? (option: 4/5/6/7)
- what is the relation between x and y
As you can see these are not the typical Data interpretation sets you face in SSC or Bank or LIC type exams.
Anyways how to approach statistical DI sets?
- In the NCERT zip file=>stat=>11_Stat_5_Measures of Central Tendency.pdf (i.e. class 11 NCERT statistics for economics –chapter 5)
- You can also go through my YouTube Playlist of Stat lectures (click me):
- In above youtube playlist page, watch video number 3,4,7,8,14,17. (Remaining topics were meant for old syllabus of UPSC General Studies mains paper II, hence useless.)
- Then solve old CDS papers.
First observe the MCQs from previous CDS exams
For this type of theory, you’ve to refer to NCERTs. In the Zip file, I’ve given separate folder for “STAT” and within that stat folder, there are two sub-folders:
|IMPORTANT||NOT SO IMPORTANT|
|Contains following NCERT chapters.|
this concludes second article, in the third and last article we’ll see how to prepare geometry, trigonometry and remaining misc. topics for the combined defense services exam.
You’ve two choices
Choice #1: good internet connection: And you want to download entire zip file at once (size 35MB) then use following link: https://files.secureserver.net/0sYHJ029rgUbrg
Choice #2: not so good internet connection: and / or You want to download small zip files or selective topics only, then goto following link (e.g. geometry zip file separately, trigonometry zip file separately and so on) then use following link: https://files.secureserver.net/0fmaNqqBDslHlc