Shannon 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 $11.50. 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¢ |
45
|
45 x 20¢ = 900¢ |
25
|
25 x 10¢ = 250¢ |
1150¢ |
$1 = 100¢
$11.50 = 1150¢
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 - 1150
= 250¢
Small difference between the value of one 20¢ coin and one 10¢ coin
= 20 - 10
= 10¢
Number of 10¢ coins
= 250 ÷ 10
= 25
Number of 20¢ coins
= 70 - 25
= 45
Answer(s): 45