Simon 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 grandmother also put on a $1 coin in the box every 7 days. The total value of the coins after 84 days was $37.40.
- How many coins were there altogether?
- How many of the coins were 20¢ coins?
Total nuber of coins that his grandmother put in
= 84 ÷ 7
= 12
Total number of coins that Simon saved
= 2 x 84 = 168 Total number of coins
= 12 + 168
= 180
(b)
Amount contributed by his grandmother
= 12 x 1
= $12
Amount that Simon saved
= 37.40 - 12
= $25.40
$1 = 100¢
$25.40 = 2540¢
Number of 20¢ coins |
Total value of 20¢ coins |
Number of 10¢ coins |
Total value of 10¢ coins |
Total value |
168
|
168 x 20 = 3360¢ |
0
|
0
|
3360¢
|
167
|
167 x 20 = 3340¢ |
1
|
1 x 10 = 10¢ |
3350¢
|
86 |
86 x 20 = 1720¢ |
82 |
82 x 10 = 820¢ |
2540¢
|
Amount that Simon saved if all he saved were 20¢ coins
= 168 x 20
= 3360
Big difference between the total values of 20¢ coins and 10¢ coins
= 3360 - 2540
= 820
Small difference between the value of 20¢ coins and 10¢ coins
= 20 - 10
= 10
Number of 10¢ coins
= 820 ÷ 10
= 82
Number of 20¢ coins
= 168 - 82
= 86
Answer(s): (a) 180; (b) 86