Ian started saving part of his pocket money by putting 2 coins in a money box every day. Each coin was either a 10¢ or 20¢ coin. His father also put on a $1 coin in the box every 7 days. The total value of the coins after 98 days was $39.80.
- How many coins were there altogether?
- How many of the coins were 20¢ coins?
Total nuber of coins that his father put in
= 98 ÷ 7
= 14
Total number of coins that Ian saved
= 2 x 98 = 196 Total number of coins
= 14 + 196
= 210
(b)
Amount contributed by his father
= 14 x 1
= $14
Amount that Ian saved
= 39.80 - 14
= $25.80
$1 = 100¢
$25.80 = 2580¢
Number of 20¢ coins |
Total value of 20¢ coins |
Number of 10¢ coins |
Total value of 10¢ coins |
Total value |
196
|
196 x 20 = 3920¢ |
0
|
0
|
3920¢
|
195
|
195 x 20 = 3900¢ |
1
|
1 x 10 = 10¢ |
3910¢
|
62 |
62 x 20 = 1240¢ |
134 |
134 x 10 = 1340¢ |
2580¢
|
Amount that Ian saved if all he saved were 20¢ coins
= 196 x 20
= 3920
Big difference between the total values of 20¢ coins and 10¢ coins
= 3920 - 2580
= 1340
Small difference between the value of 20¢ coins and 10¢ coins
= 20 - 10
= 10
Number of 10¢ coins
= 1340 ÷ 10
= 134
Number of 20¢ coins
= 196 - 134
= 62
Answer(s): (a) 210; (b) 62