Which light bulbs are cheaper per hour of light production?

Question

Carlos and John were at Wal-Mart to buy some light bulbs. They narrowed down their search to two different kinds of bulbs. The generic brand of light bulbs cost $5.00 for 4 bulbs and each bulb will produce 500 hours of light. The brand name light bulbs cost $12.00 for 6 bulbs. The brand name bulbs last 20% longer than the generic brand.

Answer 1

The generic bulb costs $5.00/4 = $1.25 per bulb

The brand name bulb costs $2.00 per bulb. The generic bulb lasts for 500 hours, hence it costs $1.25/500 = $0.0025 per hour. The brand name bulb lasts 20% more, i.e. for 600 hours and costs $2.00/600 = $0.0033 per hour. Clearly the generic bulb is cheaper per hour of light production.