The ratio between the ages of father and son is 5 : 2. If seven years ago the father was 43 years old, what is the present age of son?

How many of the numbers between 200 and 500 begin or end with 3 ?

One person sees his image in a mirror. If he walks backwards with a speed of 5 m./hour he sees his image moving with a speed of

Which is the only number other than 0 to 1 whose square root is equal to the sum of the digits ?

What should be added to 5820 so that it is divisible by 18 ?

Distance from a place A to another place B is 200 km. A car takes 3½ hours to go from A to B and 4½ hours to return from B to A. What is the average speed of the car in the whole journey?