Let us consider some examples to learn Short Tricks and Formula to solve Quantitative Aptitude Question

Example 1

The age of a father 3 years ago was 7 times the age of his son. At present the age of son is five times the age of son. What are the present age of father and son ?

Solution:

Let the present age of son = x years

the present age of father = 5x years

3 years ago

sons age = x-3

Fathers age = 5x-3

7(x-3) = 5x-3

7x-21=5x-3

2x=18

x=9

So, Present age of son is 9 years and father is 5*9=45.

Shortcut---

Sons Age = T1(x-1)/x-y= 3*(7-1)/(7-5) = 9

Example 2

A sum of money doubles itself in 10years at S.I . What is the rate of Interest.

Solution:

Let the sum be x

After 10 years it becomes 2x

Interest= Rs.2x- Rs.x =Rs.x

Rate = 100*l/P*T =100*x/x*10 = 10%

Shortcut --

Time*Rate = 100(Multiple Number of Principal Amount -1)

Rate= 100 (Multiple Number of Principal Amount-1 ) /Time

Example

A sum of money doubles itself in 7 years.In how many years will it become four fold?

shortcut --

Double in 7 years

Triple in 14 years

4 times in 21 years

5 times in 28 years

Example

When a person covers a distance between his house and office at 50 km/hr . He is late by 20 min. But when he travels at 60km/hr. He reaches 10 min early.What is the difference between his house and office ?

Solution:

Let the distance be x km

Time taken to cover x km at 50km/hr is = x/50 hrs

Time taken to cover x km at 60km/hr is = x/60 hrs

Difference between time taken = 30 min

∴x/50-x/60 = 30/60

=> 6x-5x/300 = 1/2

=> x = 150 km

Shortcut --

Required Distance = Product of two speeds / Difference of two speeds * Difference between arrival time.

So Short cut should written after solving every type of problem in a separate notebook , and remember it well.

-This kind of shortcuts saves a lot of time while solving problems.

-By following shortcut methods one can solve problems in time with high degree of accuracy