Ken started saving part of his pocket money by putting 2 coins in a money box every day. Each coin was either a 10¢ or 50¢ coin. His mother also put on a $1 coin in the box every 7 days. The total value of the coins after 70 days was $52.40.
- How many coins were there altogether?
- How many of the coins were 50¢ coins?
Total nuber of coins that his mother put in
= 70 ÷ 7
= 10
Total number of coins that Ken saved
= 2 x 70 = 140 Total number of coins
= 10 + 140
= 150
(b)
Amount contributed by his mother
= 10 x 1
= $10
Amount that Ken saved
= 52.40 - 10
= $42.40
$1 = 100¢
$42.40 = 4240¢
Number of 50¢ coins |
Total value of 50¢ coins |
Number of 10¢ coins |
Total value of 10¢ coins |
Total value |
140
|
140 x 50 = 7000¢ |
0
|
0
|
7000¢
|
139
|
139 x 50 = 6950¢ |
1
|
1 x 10 = 10¢ |
6960¢
|
71 |
71 x 50 = 3550¢ |
69 |
69 x 10 = 690¢ |
4240¢
|
Amount that Ken saved if all he saved were 50¢ coins
= 140 x 50
= 7000
Big difference between the total values of 50¢ coins and 10¢ coins
= 7000 - 4240
= 2760
Small difference between the value of 50¢ coins and 10¢ coins
= 50 - 10
= 40
Number of 10¢ coins
= 2760 ÷ 40
= 69
Number of 50¢ coins
= 140 - 69
= 71
Answer(s): (a) 150; (b) 71