Andy has 20-cent coins and 50-cent coins. The total value of all his coins is $39. He has 15 less 20-cent coins than 50-cent coins. How many coins does he have altogether?
| |
20-cent |
50-cent |
Total |
| Number |
1 u |
1 u + 15 |
2 u + 15 |
| Value |
20 |
50 |
|
| Total value |
20 u |
50 u + 750 |
70 u + 750 |
$1 = 100¢
$39 = 39 x 100 = 3900¢
Andy has 15 more 50-cent coins than 20-cent coins.
Number of 20-cent coins = 1 u
Number of 50-cent coins = 1 u + 15
Total value of 20-cent coins
= 20 x 1 u
= 20 u
Total value of 50-cent coins
= 50 x (1 u + 15)
= 50 u + 750
Total value of the coins
= 20 u + 50 u + 750
= 70 u + 750
70 u + 750 = 3900
70 u = 3900 - 750
70 u = 3150
1 u = 3150 ÷ 70 = 45
Total number of coins
= 1 u + (1 u + 15)
= 2 u + 15
= 2 x 45 + 15
= 90 + 15
= 105
Answer(s): 105
