The ratio of the number of $10-notes to $20-notes in Jen's bag was 1 : 4. Jen exchanged 7 pieces of $20-notes for $10-notes. She then had an equal number of $10-notes and $20-notes. What was the total value of $10-notes and $20-notes in Jen's bag at first?
|
$10-notes |
$20-notes |
Before |
1 u |
4 u |
Change |
+ 14 |
- 7 |
After |
1 u + 14 |
4 u - 7 |
Value of 7 pieces of $20-notes
= 7 x 20
= $140
Number of $10-notes that Jen exchanged for
= 140 ÷ 10
= 14
After the exchange, Jen had an equal number of $10-notes and $20-notes.
4 u - 7 = 1 u + 14
4 u - 1 u = 14 + 7
3 u = 21
1 u = 21 ÷ 3 = 7
Number of $10-notes at first
= 1 u
= 7
Value of $10-notes at first
= 7 x 10
= $70
Number of $20-notes at first
= 4 u
= 4 x 7
= 28
Value of $20-notes at first
= 28 x 20
= $560
Total value of $10-notes and $20-notes at first
= 70 + 560
= $630
Answer(s): $630