Carl had a total of 210 notes. The notes are $10 notes and $2 notes. After he spent 80% of the $10 notes and 60% of the $2 notes on one microwave oven, he was left with 5 times as many $2 notes as $10 notes. How much did the microwave oven cost?

	$10	$2
Before	5x2 = 10 u	5x5 = 25 u
Change	- 4x2 = - 8 u	- 3x5 = - 15 u
After	1x2 = 2 u	2x5 = 10 u
Comparing $10 and $2 in the end	1x2  = 2 u	5x2 = 10 u

80% of $10 notes = ⁸⁰
₁₀₀ of $10 notes = ⁴₅ of $10 notes
60% of $2 notes = ⁶⁰₁₀₀ of $2 notes = ³₅ of $2 notes

The number of $10 notes in the end is repeated.  Make the number of $10 notes the same.  LCM of 2 and 5 is 10.

The number of $2 notes in the end is repeated. Make the number of $2 notes the same. LCM of 1 and 2 is 2.

Number of notes at first
= 10 u + 25 u
= 35 u

35 u = 210

1 u = 210 ÷ 35 = 6

	$10	$2
Number	8 u	15 u
Value	10	2
Total value	80 u	30 u

Value of $10 spent
= 8 u x 10
= 80 u

Value of $2 spent
= 15 u x 2
= 30 u

Price of the microwave oven
= 80 u + 30 u
= 110 u
= 110 x 6
= $660

Answer(s): $660