Carl had a total of 315 notes. The notes are $5 notes and $10 notes. After he spent 80% of the $5 notes and 60% of the $10 notes on one lamp, he was left with 5 times as many $10 notes as $5 notes. How much did the lamp cost?

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

80% of $5 notes = ⁸⁰
₁₀₀ of $5 notes = ⁴₅ of $5 notes
60% of $10 notes = ⁶⁰₁₀₀ of $10 notes = ³₅ of $10 notes

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

The number of $10 notes in the end is repeated. Make the number of $10 notes the same. LCM of 1 and 2 is 2.

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

35 u = 315

1 u = 315 ÷ 35 = 9

	$5	$10
Number	8 u	15 u
Value	5	10
Total value	40 u	150 u

Value of $5 spent
= 8 u x 5
= 40 u

Value of $10 spent
= 15 u x 10
= 150 u

Price of the lamp
= 40 u + 150 u
= 190 u
= 190 x 9
= $1710

Answer(s): $1710