Shannon had some $2-notes and some $10-notes.
59 of the notes were $2-notes and the rest were $10-notes. After Shannon had spent $3900 worth of $10-notes and
45 of $2-notes, she had
17 of the notes left. Find the number of $10-notes Shannon had left.
| |
$2-notes |
$10-notes |
Total |
Comparing $2-notes
and $10-notes
at first |
5x7 =
35 u |
4x7 =
28 u |
9x7 =
63 u |
| Before |
5x7 =
35 u |
|
7x9 =
63 u |
| Change |
- 4x7 =
- 28 u |
- 390 |
- 6x9 =
- 54 u |
| After |
1x7=
7 u |
28 u - 390 |
1x9 =
9 u |
The total number of notes at first is the repeated. Make the total number of notes the same. LCM of 9 and 7 is 63.
The number of $2-notes is repeated.
Number of $10-notes
= 3900 ÷ 10
= 390
Total number of notes spent = 28 u + 390
28 u + 390 = 54 u
54 u - 28 u = 390
26 u = 390
1 u = 390 ÷ 26 = 15
Number of $10-notes that Shannon had left
= 28 u - 390
= 28 x 15 - 390
= 30
Answer(s): 30
