Carl had a total of 40 notes. The notes are $5 notes and $10 notes. After he spent 90% of the $5 notes and 60% of the $10 notes on one speaker, he was left with 4 times as many $10 notes as $5 notes. How much did the speaker cost?
|
$5 |
$10 |
Before |
10x1 = 10 u |
5x2 = 10 u
|
Change |
- 9x1 = - 9 u |
- 3x2 = - 6 u
|
After |
1x1 = 1 u |
2x2 = 4 u |
Comparing $5 and $10 in the end |
1x1 = 1 u
|
4x1 = 4 u |
90% of $5 notes =
90
100 of $5 notes =
910 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 4 is 4.
The number of $10 notes in the end is repeated. Make the number of $10 notes the same. LCM of 1 and 1 is 1.
Number of notes at first
= 10 u + 10 u
= 20 u
20 u = 40
1 u = 40 ÷ 20 = 2
|
$5 |
$10 |
Number |
9 u |
6 u |
Value |
5 |
10 |
Total value |
45 u |
60 u |
Value of $5 spent
= 9 u x 5
= 45 u
Value of $10 spent
= 6 u x 10
= 60 u
Price of the speaker
= 45 u + 60 u
= 105 u
= 105 x 2
= $210
Answer(s): $210