Explanation

Let's say the number of girls is G and the number of boys is B.

3/4G = 1/2B

Given that the total number of pupils is 1420:

G + B = 1420

Solving the equations, we get B = 852.

The correct answer is 852.

Explanation

Let A's current age be x and B's current age be y.

Since A is twice as old as B, x = 2y.

Three years ago, A's age was x - 3 and B's age was y - 3.

Since A was three times as old as B, x - 3 = 3(y - 3).

Solving the equations, we get x = 12.

So, the correct answer is 12 years.

Explanation

Since the candidate secured 60% marks, the number of questions he attempted and got correct (12) is 60% of the total questions.

So, 12 = 0.6x

x = 12 / 0.6

x = 20

Therefore, the correct answer is 20.

Explanation

To find the answer, we can use the formula: (men1 * hours1) = (men2 * hours2)

(36 * 25) = (15 * x)

x = 60 hours

Explanation