Lucy saved two coins every day from Monday to Sunday by putting them into a coin box. Each coin was either a 5¢ or 20¢ coin. The total value of the coins at the end of 6 weeks was $12.30. How many of the coins were 20¢ coins?
| 20¢ |
Value of 20¢ |
5¢ |
Value of 5¢ |
Total value |
84
|
84 x 20¢ =
1680¢ |
0 |
0 x 5¢ =
0 |
1680¢ |
83
|
83 x 20¢ =
1660¢ |
1 |
1 x 5¢ =
5¢ |
1665¢ |
54
|
54 x 20¢ =
1080¢ |
30
|
30 x 5¢ =
150¢ |
1230¢ |
$1 = 100¢
$12.30 = 1230¢
Number of coins in one week
= 2 x 7
= 14
Number of coins in 6 weeks
= 6 x 14
= 84
Total amount saved if all the coins were 20¢
= 84 x 20
= 1680¢
Big difference between the total values of 20¢ coins and 5¢ coins
= 1680 - 1230
= 450¢
Small difference between the value of one 20¢ coin and one 5¢ coin
= 20 - 5
= 15¢
Number of 5¢ coins
= 450 ÷ 15
= 30
Number of 20¢ coins
= 84 - 30
= 54
Answer(s): 54
