Sarah had some $100-notes and some $10-notes.
47 of the notes were $100-notes and the rest were $10-notes. After Sarah had spent $480 worth of $10-notes and
14 of $100-notes, she had
23 of the notes left. Find the number of $10-notes Sarah had left.
| |
$100-notes |
$10-notes |
Total |
Comparing $100-notes
and $10-notes
at first |
4x3 =
12 u |
3x3 =
9 u |
7x3 =
21 u |
| Before |
4x3 =
12 u |
|
3x7 =
21 u |
| Change |
- 1x3 =
- 3 u |
- 48 |
- 1x7 =
- 7 u |
| After |
3x3=
9 u |
9 u - 48 |
2x7 =
14 u |
The total number of notes at first is the repeated. Make the total number of notes the same. LCM of 7 and 3 is 21.
The number of $100-notes is repeated.
Number of $10-notes
= 480 ÷ 10
= 48
Total number of notes spent = 3 u + 48
3 u + 48 = 7 u
7 u - 3 u = 48
4 u = 48
1 u = 48 ÷ 4 = 12
Number of $10-notes that Sarah had left
= 9 u - 48
= 9 x 12 - 48
= 60
Answer(s): 60
