Explanation

 Let present age = x

Given:

x + 15 = 4x − 15

→ 15 + 15 = 4x − x

→ 30 = 3x

→ x = 10

Explanation

Given the total number of schools is 85:

Step 1: Calculate the number of schools completed.

Number of schools completed = 3/5 × 85

= 3 × 17

= 51

Explanation

Let the smaller number be x.

The larger number is x + 2.

Given:

x² + (x + 2)² = 100

x² + x² + 4x + 4 = 100

2x² + 4x - 96 = 0

x² + 2x - 48 = 0

(x + 8)(x - 6) = 0

x = -8 or x = 6

If x = -8, larger number = -8 + 2 = -6

If x = 6, larger number = 6 + 2 = 8

Explanation

To find the books sold in the 4th week:

Total books = 4320

Total angle in pie chart = 360°

Books sold in 4th week = 42/360 × 4320

= 4320 × 42/360

= 4320 × 7/60

= 504

Explanation

Let the younger sister's present age be x.

Fareeha's present age = x + 4

After 10 years:

Younger sister's age = x + 10

Fareeha's age = x + 4 + 10 = x + 14

Given:

x + 10 + x + 14 = 48

2x + 24 = 48

2x = 24

x = 12

Fareeha's present age = x + 4

= 12 + 4

= 16 years