Monday, April 2, 2012

Aptitude and Science Topics from Mrunal

[Aptitude] 3-in-1 Trick: Percentage change, Time n Speed, Inflation consumption, Product consistency method

Following three types of questions routinely appear in aptitude exams and all three can be solved with same "STD" formula approach.

1. If price of petrol increases by 25%, then By what percentage a person should decrease his consumption so that expenditure remains the same?
2. If Jethalal's age is 25% more than Tarak Mehta, then by What percentage is Tarak Mehta's age less than Jethalal?
3. If a car increases the speed by 25%, then by What percentage less time will you reach the destination?

All three problems can be solved quickly using our universal STD formula here.
Speed x Time = distance.
Let's concentrate on third question right now.

Time and Speed Problem

If a car increases the speed by 25%, then in how much % less time will you reach the destination?

Step 1: Put any values

Speed = 100 kmph
Time =100 hours.
Speed x time = distance.
=100 x 100 =10,000

Step 2: Increase / Decrease one thing

Now we increase the speed by 25% (given in the problem)
Speed =100+25= 125 kmph
Time= we've to find out.
Distance = same 10,000 km. (we found in Step 1)
Again use STD fomula
Speed x time = distance
125 x time = 10,000
Time = 10,000/125=80 hours.
Compare: old time was 100
New time is 80.
How much decrease?
100-80=20% decrease.
Answer: if you increase speed by 25% then time will decrease by 20%.
In the first two problems (petrol price and Jethalal), you apply the same STD fomula and you'll get the same answer.

Why does it work?

Because The product has to remains the same.
For example
6 x 4 =24
Now if you increase the 6 to 8
8 x ? =24
Obviously 4 has to decrease any become 3, because
8 x 3=24.
Because the final product has to remain consistent, if you increase one thing (price of petrol, speed of a car) then second thing (volume of petrol, journey time) must decrease to keep the product consistent.

Age problem

If Jethalal's age is 25% more than Tarak Mehta. Then by how much percentage, Tarak Mehta's age is less than Jethala?

The principle is same. Rephrase the question: if speed increased by 25%, then time will decrease by what %? Do as directed in first problem and you'll get the same answer = 20% less.

Inflation -Consumption problem

If price of petrol increases by 25%, then by how much percent must a person decrease his consumption so that expenditure remains the same?

We know that
Unit Price x quantity = total Expenditure.
e.g. if price of one ball pen is 10 rupees and you buy 10 units of pen,
the total Expenditure = 10 x 10 =100.
But to keep things simple, just remember single "STD" formula.
Speed x time =distance.
Now rephrase the question as ": if speed increased by 25%, then time will decrease by what %?
Plug in the values; you'll get the same answer from first problem. 20% decrease.

Reverse problem

If Salman khan is 50% less tall than Big B. And by what percentage Big B is taller than Salman Khan?

Rephrase: if you decreased the speed of your car by 50%, how much % more time will it take to reach destination?Read more »

[Science] Thalassaemia,Hemophilia,Leukemia & the Basics of Blood, with Mock Demo CSAT questions

In CSAT 2011, we saw a (but static) question from blood groups.
Although It is not necessary that UPSC will again ask something from blood-topic again, but a serious player should be well versed in such "Static/Theory" parts of science.
Static Question: means, it is given in the books/manuals (or indirectly related). Such question doesn't have current-affairs and can be solved easily if your basic concepts are clear.

Source : Mrunal's blog

ITCSA (Indian Telugu Civil Servants Association)