Caden 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 84 days was $38.70.
- How many coins were there altogether?
- How many of the coins were 20¢ coins?
Total nuber of coins that his father put in
= 84 ÷ 7
= 12
Total number of coins that Caden saved
= 2 x 84 = 168 Total number of coins
= 12 + 168
= 180
(b)
Amount contributed by his father
= 12 x 1
= $12
Amount that Caden saved
= 38.70 - 12
= $26.70
$1 = 100¢
$26.70 = 2670¢
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¢
|
99 |
99 x 20 = 1980¢ |
69 |
69 x 10 = 690¢ |
2670¢
|
Amount that Caden 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 - 2670
= 690
Small difference between the value of 20¢ coins and 10¢ coins
= 20 - 10
= 10
Number of 10¢ coins
= 690 ÷ 10
= 69
Number of 20¢ coins
= 168 - 69
= 99
Answer(s): (a) 180; (b) 99