Mark has 10-cent coins and 20-cent coins. The total value of all his coins is $28. He has 8 less 10-cent coins than 20-cent coins. How many coins does he have altogether?
| |
10-cent |
20-cent |
Total |
| Number |
1 u |
1 u + 8 |
2 u + 8 |
| Value |
10 |
20 |
|
| Total value |
10 u |
20 u + 160 |
30 u + 160 |
$1 = 100¢
$28 = 28 x 100 = 2800¢
Mark has 8 more 20-cent coins than 10-cent coins.
Number of 10-cent coins = 1 u
Number of 20-cent coins = 1 u + 8
Total value of 10-cent coins
= 10 x 1 u
= 10 u
Total value of 20-cent coins
= 20 x (1 u + 8)
= 20 u + 160
Total value of the coins
= 10 u + 20 u + 160
= 30 u + 160
30 u + 160 = 2800
30 u = 2800 - 160
30 u = 2640
1 u = 2640 ÷ 30 = 88
Total number of coins
= 1 u + (1 u + 8)
= 2 u + 8
= 2 x 88 + 8
= 176 + 8
= 184
Answer(s): 184
