Carl had a total of 110 notes. The notes are $2 notes and $5 notes. After he spent 90% of the $2 notes and 75% of the $5 notes on one lamp, he was left with 3 times as many $5 notes as $2 notes. How much did the lamp cost?

	$2	$5
Before	10x1 = 10 u	4x3 = 12 u
Change	- 9x1 = - 9 u	- 3x3 = - 9 u
After	1x1 = 1 u	1x3 = 3 u
Comparing $2 and $5 in the end	1x1  = 1 u	3x1 = 3 u

90% of $2 notes = ⁹⁰
₁₀₀ of $2 notes = ⁹₁₀ of $2 notes
75% of $5 notes = ⁷⁵₁₀₀ of $5 notes = ³₄ of $5 notes

The number of $2 notes in the end is repeated.  Make the number of $2 notes the same.  LCM of 1 and 3 is 3.

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
= 10 u + 12 u
= 22 u

22 u = 110

1 u = 110 ÷ 22 = 5

	$2	$5
Number	9 u	9 u
Value	2	5
Total value	18 u	45 u

Value of $2 spent
= 9 u x 2
= 18 u

Value of $5 spent
= 9 u x 5
= 45 u

Price of the lamp
= 18 u + 45 u
= 63 u
= 63 x 5
= $315

Answer(s): $315