It has to pay Rs. 225/- as bill when 9 bulbs are used for 30 days using them for 4 hours per day. Find the number of days if 5 bulbs are used for 6 hours per day for the payment of Rs. 375/- against the bill.

Question

Question

This question was previously asked in

WBPSC Miscellaneous Preliminary Exam 2012 Official Paper (Held On 19th May 2013 Shift 1)

Answer 1

Given:

The cost of using 9 bulbs for 30 days for 4 hours per day is Rs. 225.

We are to calculate for 5 bulbs used for 6 hours per day with a total cost of Rs. 375

Solution:

the total cost of electricity in terms of bulb-hours per day (bulbs × hours per day × days).

The total bulb-hours for the Rs. 225 payment are 9 bulbs × 4 hours/day × 30 days = 1080 bulb-hours.

The cost per bulb-hour can be calculated as Rs. 225 / 1080 bulb-hours = Rs. 0.2083 per bulb-hour.

the number of days.

⇒ Rs. 375 / (Rs. 0.2083 per bulb-hour) × (1 day / (5 bulbs × 6 hours/day)) = approximately 60 days

Hence, the correct answer is 60 days.

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