Prologue
 In the previous article, we saw how to prepare number system, surdsindices, linear and quadratic equations for CDS maths paper. click me
 Now in this second article, weâll see how to approach percentage, profitloss, simplecompound interest rate, timespeeddistancework and statisticsData interpretation related problems.
 In the third article, weâll see how to approach geometry, trigonometry and remaining misc. Topics. click me
[Block#2] %, STD and Stat
topics in this block  avg. MCQs in each of the last four CDS exams.  priority 
Profit loss, SICI, ratioproportion  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 â5â only because in earlier times, they used to ask a lot from here. Still 23 MCQs are good because you hardly need to memorize any formulas.
Percentages, Profit loss SICI
Unlike the IBPS questions, here % or compound interest rate doesnât require lengthy multiplication or division. Most of the time the numerators will be easily cut.
NCERT  
7_8 Comparing Quantities  introduces to %, simple interest rates, profit  IAK 
8_8 Comparing Quantities  compound interest rates  IAK* 
* IAK=âI already knowâ. Meaning you can ignore this chapter, if youâre basics are already good. (i.e. youâve 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 (ProfitLoss) without (stupid) formulas
 Compound Interest Rate, Population Growth without Formulas
 Alligation: Advanced applications in Interest rates, Profitloss, Average Wages (WineWater 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 %, TimeSpeedDistance problems,
Then do Sarvesh Kumarâs 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 âloaninstallmentâ related problems because I didnât see them in last 5 yearsâ 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 secondyear 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  PROFITLOSSMARKED PRICE & DISCOUNT 


Ratio Proportion
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 theyâre 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 profitsharing made Easy.
Demo MCQs from previous CDS exams
RATIO: TWO ENTITIES  RATIO: THREE ENTITIES 


INCOME EXPENSE  VARIATION 


Time speed distance Work (TSDW)
In this portion, NCERT not much useful because it runs on the LCM method and doesnât 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 âA can complete a work inâŚ.â, âpipe A can fill the tank in âŚâ etc.
All of these can be solved through just one formula: STD (speed x time =distance). Go through following articles:
Once youâve got the idea of STD method, solve all the examples and questions given in Sarvesh Kumarâs 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 


MDW related  

StatisticsData interpretation (DI)
average 6MCQ per exam in last four exams from this section. But in the CDS maths paper, the statisticsDI portion differs from SSCCGL / IBPS type exams because
 Theory / definition based MCQs asked.
 For data interpretation they donât ask conventional piechart, bargraph related cases. Instead they give frequency chart and youâve to find mean / median / mode. (i.e. like the âstatâ portion in the UPSC GS mains paper II under old syllabus.) Therefore youâve to mugup those special formulas for continuous series etc.
Stat#1: Calculation type
first observe the MCQs
Weighted averageÂ (winewater)  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 (winewater)  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, Iâve 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.
youâll also find a few MCQs of GM, HM in Sarvesh Kumarâs chapter on âSequence, series and progressionsâ.
Stat#2: Data Interpretation sets
First Observe the MCQs from past exams
Q1. Consider following data
x  1  2  3  4  5 
f  3  5  9  A  2 
IF THE arithmetic mean is 2.96, what is the missing frequency âAâ? (options: 4/6/7/8)
Q2. Consider following data
class interval  110  1120  2130  3140  4150  5150  
frequency  9  22  –  20  12  8  100 total frequency 
What is the modal class?
 10.5 to 20.5 only
 10.520.5Â and 20.530.5
 20.530.5 only
 there is modal class
Q3. for the following table, median is 14.4 and total frequency is 20.
class  06  612  1218  1824  2430 
fr.  4  x  5  y  1 
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
 2x=3y
 3x=2y
 x=y
 2x=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 âchapter 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.
Stat#3: Theory / definition type MCQs
First observe the MCQs from previous CDS exams


For this type of theory, youâve to refer to NCERTs. In the Zip file, Iâve given separate folder for âSTATâ and within that stat folder, there are two subfolders:
IMPORTANT  NOT SO IMPORTANT 
Contains following NCERT chapters.


this concludes second article, in the third and last article weâll see how to prepare geometry, trigonometry and remaining misc. topics for the combined defense services exam.
Appendix Download link: Topic wise Sorted NCERTs
Youâve 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