Xuan saved two coins every day from Monday to Sunday by putting them into a glass jar. Each coin was either a 10¢ or 20¢ coin. The total value of the coins at the end of 5 weeks was $10.80. How many of the coins were 20¢ coins?
| 20¢ |
Value of 20¢ |
10¢ |
Value of 10¢ |
Total value |
70
|
70 x 20¢ =
1400¢ |
0 |
0 x 10¢ =
0 |
1400¢ |
69
|
69 x 20¢ =
1380¢ |
1 |
1 x 10¢ =
10¢ |
1390¢ |
38
|
38 x 20¢ =
760¢ |
32
|
32 x 10¢ =
320¢ |
1080¢ |
$1 = 100¢
$10.80 = 1080¢
Number of coins in one week
= 2 x 7
= 14
Number of coins in 5 weeks
= 5 x 14
= 70
Total amount saved if all the coins were 20¢
= 70 x 20
= 1400¢
Big difference between the total values of 20¢ coins and 10¢ coins
= 1400 - 1080
= 320¢
Small difference between the value of one 20¢ coin and one 10¢ coin
= 20 - 10
= 10¢
Number of 10¢ coins
= 320 ÷ 10
= 32
Number of 20¢ coins
= 70 - 32
= 38
Answer(s): 38
