Justin has 5-cent coins and 10-cent coins. The total value of all his coins is $39. He has 12 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 + 12 |
2 u + 12 |
Value |
5 |
10 |
|
Total value |
5 u |
10 u + 120 |
15 u + 120 |
$1 = 100¢
$39 = 39 x 100 = 3900¢
Justin has 12 more 10-cent coins than 5-cent coins.
Number of 5-cent coins = 1 u
Number of 10-cent coins = 1 u + 12
Total value of 5-cent coins
= 5 x 1 u
= 5 u
Total value of 10-cent coins
= 10 x (1 u + 12)
= 10 u + 120
Total value of the coins
= 5 u + 10 u + 120
= 15 u + 120
15 u + 120 = 3900
15 u = 3900 - 120
15 u = 3780
1 u = 3780 ÷ 15 = 252
Total number of coins
= 1 u + (1 u + 12)
= 2 u + 12
= 2 x 252 + 12
= 504 + 12
= 516
Answer(s): 516