Nora saved two coins every day from Monday to Sunday by putting them into a glass jar. Each coin was either a 5¢ or 20¢ coin. The total value of the coins at the end of 5 weeks was $10.40. How many of the coins were 20¢ coins?
20¢ |
Value of 20¢ |
5¢ |
Value of 5¢ |
Total value |
70
|
70 x 20¢ = 1400¢ |
0 |
0 x 5¢ = 0 |
1400¢ |
69
|
69 x 20¢ = 1380¢ |
1 |
1 x 5¢ = 5¢ |
1385¢ |
46
|
46 x 20¢ = 920¢ |
24
|
24 x 5¢ = 120¢ |
1040¢ |
$1 = 100¢
$10.40 = 1040¢
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 5¢ coins
= 1400 - 1040
= 360¢
Small difference between the value of one 20¢ coin and one 5¢ coin
= 20 - 5
= 15¢
Number of 5¢ coins
= 360 ÷ 15
= 24
Number of 20¢ coins
= 70 - 24
= 46
Answer(s): 46