Paul has 10-cent coins and 20-cent coins. The total value of all his coins is $30. He has 15 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 + 15 |
2 u + 15 |
Value |
10 |
20 |
|
Total value |
10 u |
20 u + 300 |
30 u + 300 |
$1 = 100¢
$30 = 30 x 100 = 3000¢
Paul has 15 more 20-cent coins than 10-cent coins.
Number of 10-cent coins = 1 u
Number of 20-cent coins = 1 u + 15
Total value of 10-cent coins
= 10 x 1 u
= 10 u
Total value of 20-cent coins
= 20 x (1 u + 15)
= 20 u + 300
Total value of the coins
= 10 u + 20 u + 300
= 30 u + 300
30 u + 300 = 3000
30 u = 3000 - 300
30 u = 2700
1 u = 2700 ÷ 30 = 90
Total number of coins
= 1 u + (1 u + 15)
= 2 u + 15
= 2 x 90 + 15
= 180 + 15
= 195
Answer(s): 195