Oscar 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 grandfather also put on a $1 coin in the box every 7 days. The total value of the coins after 105 days was $64.80.
- How many coins were there altogether?
- How many of the coins were 50¢ coins?
Total nuber of coins that his grandfather put in
= 105 ÷ 7
= 15
Total number of coins that Oscar saved
= 2 x 105 = 210 Total number of coins
= 15 + 210
= 225
(b)
Amount contributed by his grandfather
= 15 x 1
= $15
Amount that Oscar saved
= 64.80 - 15
= $49.80
$1 = 100¢
$49.80 = 4980¢
Number of
50¢ coins |
Total value
of 50¢ coins |
Number of
10¢ coins |
Total value
of 10¢ coins |
Total value |
210
|
210 x 50
= 10500¢ |
0
|
0
|
10500¢
|
209
|
209 x 50
= 10450¢ |
1
|
1 x 10 =
10¢ |
10460¢
|
| 72 |
72 x 50
= 3600¢ |
138 |
138 x 10 =
1380¢ |
4980¢
|
Amount that Oscar saved if all he saved were 50¢ coins
= 210 x 50
= 10500
Big difference between the total values of 50¢ coins and 10¢ coins
= 10500 - 4980
= 5520
Small difference between the value of 50¢ coins and 10¢ coins
= 50 - 10
= 40
Number of 10¢ coins
= 5520 ÷ 40
= 138
Number of 50¢ coins
= 210 - 138
= 72
Answer(s): (a) 225; (b) 72
