Question

A lamp lighter has to light 50gas lamps.He takes 3 minutes to go from one lamp post to the next.Each lamp burns 20 cubic feet of gas per hour.How many cubic feet of gas have been burnt by 9pm.If he starts the first post by 6pm.​

Answer 1

Step-by-step explanation:

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Answer 2

Step-by-step explanation:

Each lamp burns 10 cubic ft. of gas/hr.

$each \: lamp \: burns \frac{10}{60} \: = \frac{1}{6} cubic \: ft \div min$

Number of hours from 6 p.m. to 8:30 = 2.5 hrs = 150 minutes

He takes 1.5 minutes to go from one lamp to another.

So, 1st lamp will burn for 150 minutes

2nd lamp will burn for (150 – 1.5) min = 148.5

3rd lamp will burn for (148.5 – 1.5) min = 147

$= > gas \: used = \frac{1}{6} (15 0 + 148.5 + 147 + ........ + 1.5)$

$= \frac{1}{6} \times \frac{100}{2} (150 + 1.5)$

$a(150 + 148.5 + ...... + 1.5) \: form \: or \: ap \: with \: common \: difference \: 1.5 \: and \: number \: of \: term \: = 100$

= 1262.5 cubic feet