Question

A heater boils certain amount of water in 15 minute. Another heater boils same amount of water in 10 minute. Time taken to boil same amount of water when both are used in series?

Answer 1

Given that First heater boils certain amount of water in 15 minutes.

Another heater boils it in 10 minutes.

Let water boiled by both of them in one minute be 1 / x

Amount boiled by first heater in 1 minute = 1 / 15

Water boiled by another heater = 1 / 10

so the equation forms in this way :

1 / 15 + 1 / 10 = 1 / x

L.C.M = 30

1 × 2 / 15 × 2 + 3 × 1 / 10 × 3 = 1 / x

2 + 3 / 30 = 1 / x

5 / 30 = 1 / x

Cross multiply the fractions

5 × x = 1 × 30

5x = 30

x = 30 / 5

x = 6

So time taken by both the heaters to boil the water is 6 minutes.

So the answer is 6 minutes.

Hope it helps you buddy.

Answer 2

time taken by both first and second heater is 6 minutes