There were a total of thirty 20-cent coins and 50-cent coins in a bag. Given that the total amount of money in the bag was $12.90. How many 20-cent coins were there in the bag?
Number of 50-cent coins |
Value of 50-cent coins |
Number of 20-cent coins |
Value of 20-cent coins |
Total value |
30
|
30 x 50 = 1500¢ |
0
|
0
|
1500¢
|
29
|
29 x 50 = 1450¢ |
1
|
1 x 20 = 20¢ |
1470¢
|
23
|
23 x 50 = 1150¢ |
7
|
7 x 20 = 140¢ |
1290¢ |
$1 = 100¢
$12.90 = 1290¢
Amount in the bag if all are 50-cent coins
= 30 x 50
= 1500¢
Big difference between the value of 50-cent coins and 20-cent coins
= 1500 - 1290
= 210¢
Small difference between the value of one 50-cent coin and one 20-cent coin
= 50 - 20
= 30¢
Number of 20-cent coins
= 210 ÷ 30
= 7
Answer(s): 7