Albert has 10-cent coins and 20-cent coins. The total value of all his coins is $38. He has 7 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 + 7 |
2 u + 7 |
Value |
10 |
20 |
|
Total value |
10 u |
20 u + 140 |
30 u + 140 |
$1 = 100¢
$38 = 38 x 100 = 3800¢
Albert has 7 more 20-cent coins than 10-cent coins.
Number of 10-cent coins = 1 u
Number of 20-cent coins = 1 u + 7
Total value of 10-cent coins
= 10 x 1 u
= 10 u
Total value of 20-cent coins
= 20 x (1 u + 7)
= 20 u + 140
Total value of the coins
= 10 u + 20 u + 140
= 30 u + 140
30 u + 140 = 3800
30 u = 3800 - 140
30 u = 3660
1 u = 3660 ÷ 30 = 122
Total number of coins
= 1 u + (1 u + 7)
= 2 u + 7
= 2 x 122 + 7
= 244 + 7
= 251
Answer(s): 251