Vaidev has a total of 15 twenty-cent and ten-cent coins. The total value of the coins is $2. If he spends all the twenty-cent coins on a pen, how much does the pen cost?
Number of
twenty-cent coins |
Value of
twenty-cent coins |
Number of
ten-cent coins |
Value of
ten-cent coins |
Total
value |
| 15 |
15 x 20
= 300¢ |
0 |
0 |
300¢ |
| 14 |
14 x 20
= 280¢ |
1 |
1 x 10
= 10¢ |
290¢ |
| 5 |
5 x 20
= 100¢ |
10 |
10 x 10
= 100¢ |
200¢ |
$1 = 100¢
$2 = 200¢
Total value if all the coins are twenty-cent coins
= 15 x 20
= 300¢
Big difference between the value of twenty-cent coins and ten-cent coins
= 300 - 200
= 100¢
Small difference between the value of one twenty-cent coin and one ten-cent coin
= 20 - 10
= 10¢
Number of ten-cent coins
= 100 ÷ 10
= 10
Number of twenty-cent coins
= 15 - 10
= 5
Cost of the pen
= 5 x 20
= 100¢
= $1
Answer(s): $1
