Tommy has 5-cent coins and 10-cent coins. The total value of all his coins is $21. He has 3 less 5-cent coins than 10-cent coins. How many coins does he have altogether?
|
5-cent |
10-cent |
Total |
Number |
1 u |
1 u + 3 |
2 u + 3 |
Value |
5 |
10 |
|
Total value |
5 u |
10 u + 30 |
15 u + 30 |
$1 = 100¢
$21 = 21 x 100 = 2100¢
Tommy has 3 more 10-cent coins than 5-cent coins.
Number of 5-cent coins = 1 u
Number of 10-cent coins = 1 u + 3
Total value of 5-cent coins
= 5 x 1 u
= 5 u
Total value of 10-cent coins
= 10 x (1 u + 3)
= 10 u + 30
Total value of the coins
= 5 u + 10 u + 30
= 15 u + 30
15 u + 30 = 2100
15 u = 2100 - 30
15 u = 2070
1 u = 2070 ÷ 15 = 138
Total number of coins
= 1 u + (1 u + 3)
= 2 u + 3
= 2 x 138 + 3
= 276 + 3
= 279
Answer(s): 279