Quantitative Aptitude - Arithmetic Ability Questions

Here the order of choosing the elements doesn’t matter and this is a problem in combinations.

We have to find the number of ways of choosing 4 elements of this set which has 11 elements.

This can be done in 11C4 ways = 330 ways

Let Kumar’s present age be "x" years and Sailesh’s present age be "y" years.
Then, according to the first condition,

x - 10 = 3(y - 10) => x - 3y = - 20 ........(1)

Now, Kumar’s age after 10 years = (x + 10) years.

Sailesh’s age after 10 years = (y + 10) years.

(x + 10) = 2 (y + 10)  => x - 2y = 10 ......(2)

Solving (1) and (2),

we get x = 70 and y = 30

Kumar’s present age = 70 years    and  Sailesh’s present age = 30 years.

Number of bricks = volume of the wall/volume of one brick 

= (800 x 600 x 22.5)/(25 x 11.25 x 6 )= 6400

Let the number  of 20 paise coins be x. Then the no of 25 paise coins = (324 - x).

0.20 * (x) + 0.25 (324 - x) = 71 => x = 200..

Given ratio of pens and pencils = 3 :2

Number of Pens = 3x

Number of Pencils = 2x

Average number of pencils & Pens = 3x + 2x2 = 180

5x = 360

=> x = 72

Hence, the number of pencils = 2x = 72 x 2 = 144.