Explanation

• Speed = 12 km/h
• Time = 15 minutes = 15/60 = 1/4 hour

Formula:

Distance = Speed x Time 

= 12 x 1/4

$$= 12 times frac{1}{4}$$ =3 km

Explanation

Let the present age of the son = x years.

Present age of the father = 45 − x years.

5 years ago:

Father's age = 40 − x

Son's age = x − 5

According to the question:

40 − x = 6(x − 5)

40 − x = 6x − 30

70 = 7x

x = 10

Son's present age = 10 years.

Father's present age = 45 − 10 = 35 years.

Last verified on 08-10-2026

Explanation

Total work = 72 workers 40 days = 2880 worker-days

For 64 workers:

Days = 2880 / 64 = 45 days

Last verified on 07-10-2026

Explanation

Let son's age now = x

Father's age now = 4x

After 20 years:

Son = x + 20

Father = 4x + 20

According to question:

4x + 20 = 2 * (x + 20)

4x + 20 = 2x + 40

4x - 2x = 40 - 20

2x = 20

x = 10

Son is 10 years old now (Father is 40).

Last verified on 07-10-2026

Explanation

Given:

• Train length = 90 m
• Tunnel length = 231 m
• Time = 11 seconds

Distance covered = 90 + 231 = 321 m

Speed = Distance ÷ Time
= 321 ÷ 11 = 29.18 m/s

Convert to km/h:

29.18 × 18/5 = 105.05 km/h