Carl had a total of 112 notes. The notes are $10 notes and $5 notes. After he spent 75% of the $10 notes and 60% of the $5 notes on one microwave oven, he was left with 4 times as many $5 notes as $10 notes. How much did the microwave oven cost?

	$10	$5
Before	4x1 = 4 u	5x2 = 10 u
Change	- 3x1 = - 3 u	- 3x2 = - 6 u
After	1x1 = 1 u	2x2 = 4 u
Comparing $10 and $5 in the end	1x1  = 1 u	4x1 = 4 u

75% of $10 notes = ⁷⁵
₁₀₀ of $10 notes = ³₄ of $10 notes
60% of $5 notes = ⁶⁰₁₀₀ of $5 notes = ³₅ of $5 notes

The number of $10 notes in the end is repeated.  Make the number of $10 notes the same.  LCM of 2 and 4 is 4.

The number of $5 notes in the end is repeated. Make the number of $5 notes the same. LCM of 1 and 1 is 1.

Number of notes at first
= 4 u + 10 u
= 14 u

14 u = 112

1 u = 112 ÷ 14 = 8

	$10	$5
Number	3 u	6 u
Value	10	5
Total value	30 u	30 u

Value of $10 spent
= 3 u x 10
= 30 u

Value of $5 spent
= 6 u x 5
= 30 u

Price of the microwave oven
= 30 u + 30 u
= 60 u
= 60 x 8
= $480

Answer(s): $480