A father is now three times as old as his son. Five years back, he was four times as old as his son. The age of the son (in years) is

When Ravi's brother was born, let Ravi's father's age = x years and mother's age = y years.

Then, sister's age = (x - 28) years. So, x - 28 = 4 or x = 32.

Ravi's age = (y - 26) years. Age of Ravi's brother = (y - 26 + 3) years = (y - 23) years.

Now, when Ravi's brother was born, his age = 0 i.e. y - 23 = 0 or y = 23.

We have : A = 3B ...(i) and

C - 4 = 2 (A - 4) ...(ii)

Also, A + 4 = 31 or A= 31-4 = 27.

Putting A = 27 in (i), we get: B = 9.

Putting A = 27 in (ii), we get C = 50.

Since one of the numbers on the dial of a telephone is zero, so the product of all the numbers on it is 0.

Since there are socks of only two colours, so two out of any three socks must always be of the same colour.

Originally, let number of women = x. Then, number of men = 2x.

So, in city Y, we have : (2x - 10) = (x + 5) or x - 15.

Therefore Total number of passengers in the beginning = (x + 2x) = 3x = 45.

Let the number of boys and girls participating in sports be 3x and 2x respectively.

Then, 3x = 15 or x = 5.

So, number of girls participating in sports = 2x = 10.

Number of students not participating in sports = 60 - (15 + 10) = 35.

Let number of boys not participating in sports be y.

Then, number of girls not participating in sports = (35 -y).

Therefore (35 - y) = y + 5 ⟺ 2y ⟺ 30 ⟺ y = 15.

So, number of girls not participating in sports = (35 - 15) = 20.

Hence, total number of girls in the class = (10 + 20) = 30.

'All but nine died' means 'All except nine died' i.e. 9 sheep remained alive.