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# prolem solving question Watch

1. I'm having a tought time solving this problem:
The 100W light bulb (cost €0.60) is not going to be used anymore and is being replaced with the
20W (cost €3) low energy light bulb.

If electricity is charged at €0.15 per kWh, for how many hours must the low energy bulb be used in
order for the lower cost of running it to exactly compensate for its higher initial cost?

A 160.00
B 0.25
C 200.00
D 250.00
E 720.00

The correct answer is A but I can't seem to understand why, I keep getting C.
here's my thought process:

100W/h=0.01kWh, 20W/h=0.02kWh
0.1*0.15=0.015€/h, 0.02*0.15=0.003€/h
t- amount of hours running
(0.015*t)+0.6=(0.003*t)+3
0.012t=2.4
t=200
2. How long can you use 80W and it cost 2.40

2.4/0.15 = 16 KWh = 16000 Wh

16000/80 = 200 hours

I agree with you
3. Solve

I get
4. Thanks for helping guys.
So there is no way that the answer is A even though it the official answer on the answer key?
5. (Original post by alextav)
Thanks for helping guys.
So there is no way that the answer is A even though it the official answer on the answer key?
doesn't look like it

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