Liam has 10-cent coins and 20-cent coins. The total value of all his coins is $21. He has 18 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 + 18 |
2 u + 18 |
| Value |
10 |
20 |
|
| Total value |
10 u |
20 u + 360 |
30 u + 360 |
$1 = 100¢
$21 = 21 x 100 = 2100¢
Liam has 18 more 20-cent coins than 10-cent coins.
Number of 10-cent coins = 1 u
Number of 20-cent coins = 1 u + 18
Total value of 10-cent coins
= 10 x 1 u
= 10 u
Total value of 20-cent coins
= 20 x (1 u + 18)
= 20 u + 360
Total value of the coins
= 10 u + 20 u + 360
= 30 u + 360
30 u + 360 = 2100
30 u = 2100 - 360
30 u = 1740
1 u = 1740 ÷ 30 = 58
Total number of coins
= 1 u + (1 u + 18)
= 2 u + 18
= 2 x 58 + 18
= 116 + 18
= 134
Answer(s): 134
