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light bulbs.

by nasir » Sat Jul 02, 2011 11:22 pm
A number of light bulbs were purchased to illuminate a gym. However, only 2/3 of them were needed and 160 leftover light bulbs were returned. If only 60% percent of their cost, or $96, was reimbursed, how much money was spent on illuminating the gym ?

How to find cost of each bulb .
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by MBA.Aspirant » Sat Jul 02, 2011 11:44 pm
nasir wrote:A number of light bulbs were purchased to illuminate a gym. However, only 2/3 of them were needed and 160 leftover light bulbs were returned. If only 60% percent of their cost, or $96, was reimbursed, how much money was spent on illuminating the gym ?

How to find cost of each bulb .
THanks
let number of bulbs be n

1/3 n = 160

n = 480

60% of 160 bulbs cost = 96

cost = 96/0.6 = 160

cost per bulb = 160/160 = 1$
cost of illumnating the gym = (480 - 160 ) * 1 = 320 $
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by Geva@EconomistGMAT » Sat Jul 02, 2011 11:54 pm
nasir wrote:A number of light bulbs were purchased to illuminate a gym. However, only 2/3 of them were needed and 160 leftover light bulbs were returned. If only 60% percent of their cost, or $96, was reimbursed, how much money was spent on illuminating the gym ?

How to find cost of each bulb .
THanks
formulate a defining sentence: $96 is 60% of cost.

Then translate into an equation using a translation key from left to right:

"is" means "="
"%" means "over a 100, or /100. So '60%' becomes '60/100'
'of' means '*'

translation:
96=60/100*cost.

Isolate cost by mutiplying times 100/60
96*100/60 = cost
Reduce zero and 6 to get
16*10 =$160

Approach 2: use 10% blocks: Move from 60% to 10%, and then from 10% to 100%.

If $96 is 60%, then 10% would be one sixth of $96: 966 = 16.

If 10% is $16, then 100% is 10 times 10%, or 16*10 = 160.
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