Perry has 10-cent coins and 20-cent coins. The total value of all his coins is $18. He has 12 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 + 12 |
2 u + 12 |
Value |
10 |
20 |
|
Total value |
10 u |
20 u + 240 |
30 u + 240 |
$1 = 100¢
$18 = 18 x 100 = 1800¢
Perry has 12 more 20-cent coins than 10-cent coins.
Number of 10-cent coins = 1 u
Number of 20-cent coins = 1 u + 12
Total value of 10-cent coins
= 10 x 1 u
= 10 u
Total value of 20-cent coins
= 20 x (1 u + 12)
= 20 u + 240
Total value of the coins
= 10 u + 20 u + 240
= 30 u + 240
30 u + 240 = 1800
30 u = 1800 - 240
30 u = 1560
1 u = 1560 ÷ 30 = 52
Total number of coins
= 1 u + (1 u + 12)
= 2 u + 12
= 2 x 52 + 12
= 104 + 12
= 116
Answer(s): 116