<PRE><B>Question 1176181</B>
The owner of a hobby store bought a case of 9-volt batteries for $53.80.
 He marked the price up such that his profit was $3.05 per battery. 
Once he had sold 15 batteries, the store owner had recovered his cost.
 How many 9-volt batteries are in a case? 110, 95,100, or 105?
:
let n = no. batteries in the case
:
{{{53.80/n)}}} = his cost for each battery
:
3.05(15) + 15({{{53.80/n}}}) = 53.80
45.75 + {{{807/n}}} = 53.80
multiply eq by n
45.75n + 807 = 53.80n
807 = 53.80n - 45.75n
807 = 8.05n
n = 807/8.05
n = 100.25 ~ 100 in a case
:
See if that checks out
cost of each battery 53.80/100 = .538 ~ 54 cents
Profit on each given as 3.05
Price of each battery 3.05 + 54 = $3.59
Sale of 15 batteries: 15 * 3.59 = $53.85, recovered his cost
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