Mark 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 42 days was $42.80.
- How many coins were there altogether?
- How many of the coins were 50¢ coins?
Total nuber of coins that his mother put in
= 42 ÷ 7
= 6
Total number of coins that Mark saved
= 2 x 42 = 84 Total number of coins
= 6 + 84
= 90
(b)
Amount contributed by his mother
= 6 x 1
= $6
Amount that Mark saved
= 42.80 - 6
= $36.80
$1 = 100¢
$36.80 = 3680¢
Number of 50¢ coins |
Total value of 50¢ coins |
Number of 10¢ coins |
Total value of 10¢ coins |
Total value |
84
|
84 x 50 = 4200¢ |
0
|
0
|
4200¢
|
83
|
83 x 50 = 4150¢ |
1
|
1 x 10 = 10¢ |
4160¢
|
71 |
71 x 50 = 3550¢ |
13 |
13 x 10 = 130¢ |
3680¢
|
Amount that Mark saved if all he saved were 50¢ coins
= 84 x 50
= 4200
Big difference between the total values of 50¢ coins and 10¢ coins
= 4200 - 3680
= 520
Small difference between the value of 50¢ coins and 10¢ coins
= 50 - 10
= 40
Number of 10¢ coins
= 520 ÷ 40
= 13
Number of 50¢ coins
= 84 - 13
= 71
Answer(s): (a) 90; (b) 71