Lamplit has to light 100 gas lamps. It takes 60 seconds to travel from one lamppost to the next. Each lamp burns 12 cubic feet of gas per hour. If he lights the first lamp at 7 pm, then how much gas will be burnt by the time he lights the last?
Lamplit has to light 100 gas lamps. It takes 60 seconds to travel from one lamppost to the next. Each lamp burns 12 cubic feet of gas per hour. If he lights the first lamp at 7 pm, then how much gas will be burnt by the time he lights the last? Correct Answer 990 cubic feet
Given:
Lamplit has to light 100 gas lamps.
It takes 60 seconds to travel from one lamppost to the next.
Each lamp burns 12 cubic feet of gas per minute.
Calculation:
Each lamp burns 12 cubic feet of gas per hour
In one minute = 12/60
⇒ 1/5 cubic feet gas per minute
According to the question,
He takes 1 min. to go from one lamp post to the other.
When he lights the last lamp post, the first lamppost will burn for 99 minutes, the second for 98 minutes, so on
Gas used = (1/5)(99 + 98 + 97 + ....... + 1)
⇒ (100 × 99)/(2 × 5)
⇒ 990 cubic feet.
∴ Gas will be burnt by the time he lights the last 990 cubic feet.
