Justin has 5-cent coins and 10-cent coins. The total value of all his coins is $39. 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¢
$39 = 39 x 100 = 3900¢
Justin 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 = 3900
15 u = 3900 - 30
15 u = 3870
1 u = 3870 ÷ 15 = 258
Total number of coins
= 1 u + (1 u + 3)
= 2 u + 3
= 2 x 258 + 3
= 516 + 3
= 519
Answer(s): 519
