Mark has 10-cent coins and 50-cent coins. The total value of all his coins is $27. He has 18 less 10-cent coins than 50-cent coins. How many coins does he have altogether?
| |
10-cent |
50-cent |
Total |
| Number |
1 u |
1 u + 18 |
2 u + 18 |
| Value |
10 |
50 |
|
| Total value |
10 u |
50 u + 900 |
60 u + 900 |
$1 = 100¢
$27 = 27 x 100 = 2700¢
Mark has 18 more 50-cent coins than 10-cent coins.
Number of 10-cent coins = 1 u
Number of 50-cent coins = 1 u + 18
Total value of 10-cent coins
= 10 x 1 u
= 10 u
Total value of 50-cent coins
= 50 x (1 u + 18)
= 50 u + 900
Total value of the coins
= 10 u + 50 u + 900
= 60 u + 900
60 u + 900 = 2700
60 u = 2700 - 900
60 u = 1800
1 u = 1800 ÷ 60 = 30
Total number of coins
= 1 u + (1 u + 18)
= 2 u + 18
= 2 x 30 + 18
= 60 + 18
= 78
Answer(s): 78
