Billy has 10-cent coins and 20-cent coins. The total value of all his coins is $15. He has 3 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 + 3 |
2 u + 3 |
Value |
10 |
20 |
|
Total value |
10 u |
20 u + 60 |
30 u + 60 |
$1 = 100¢
$15 = 15 x 100 = 1500¢
Billy has 3 more 20-cent coins than 10-cent coins.
Number of 10-cent coins = 1 u
Number of 20-cent coins = 1 u + 3
Total value of 10-cent coins
= 10 x 1 u
= 10 u
Total value of 20-cent coins
= 20 x (1 u + 3)
= 20 u + 60
Total value of the coins
= 10 u + 20 u + 60
= 30 u + 60
30 u + 60 = 1500
30 u = 1500 - 60
30 u = 1440
1 u = 1440 ÷ 30 = 48
Total number of coins
= 1 u + (1 u + 3)
= 2 u + 3
= 2 x 48 + 3
= 96 + 3
= 99
Answer(s): 99