The ratio of the number of $10-notes to $20-notes in Mary's handbag was 1 : 6. Mary exchanged 5 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 Mary's handbag at first?
|
$10-notes |
$20-notes |
Before |
1 u |
6 u |
Change |
+ 10 |
- 5 |
After |
1 u + 10 |
6 u - 5 |
Value of 5 pieces of $20-notes
= 5 x 20
= $100
Number of $10-notes that Mary exchanged for
= 100 ÷ 10
= 10
After the exchange, Mary had an equal number of $10-notes and $20-notes.
6 u - 5 = 1 u + 10
6 u - 1 u = 10 + 5
5 u = 15
1 u = 15 ÷ 5 = 3
Number of $10-notes at first
= 1 u
= 3
Value of $10-notes at first
= 3 x 10
= $30
Number of $20-notes at first
= 6 u
= 6 x 3
= 18
Value of $20-notes at first
= 18 x 20
= $360
Total value of $10-notes and $20-notes at first
= 30 + 360
= $390
Answer(s): $390