Risa had some $1-notes and some $10-notes.
512 of the notes were $1-notes and the rest were $10-notes. After Risa had spent $9690 worth of $10-notes and
35 of $1-notes, she had
411 of the notes left. Find the number of $10-notes Risa had left.
| |
$1-notes |
$10-notes |
Total |
Comparing $1-notes
and $10-notes
at first |
5x11 =
55 u |
7x11 =
77 u |
12x11 =
132 u |
| Before |
5x11 =
55 u |
|
11x12 =
132 u |
| Change |
- 3x11 =
- 33 u |
- 969 |
- 7x12 =
- 84 u |
| After |
2x11=
22 u |
77 u - 969 |
4x12 =
48 u |
The total number of notes at first is the repeated. Make the total number of notes the same. LCM of 12 and 11 is 132.
The number of $1-notes is repeated.
Number of $10-notes
= 9690 ÷ 10
= 969
Total number of notes spent = 33 u + 969
33 u + 969 = 84 u
84 u - 33 u = 969
51 u = 969
1 u = 969 ÷ 51 = 19
Number of $10-notes that Risa had left
= 77 u - 969
= 77 x 19 - 969
= 494
Answer(s): 494
