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 20¢ coin. His father also put on a $1 coin in the box every 7 days. The total value of the coins after 42 days was $22.10.
- How many coins were there altogether?
- How many of the coins were 20¢ coins?
Total nuber of coins that his father put in
= 42 ÷ 7
= 6
Total number of coins that Oscar saved
= 2 x 42 = 84 Total number of coins
= 6 + 84
= 90
(b)
Amount contributed by his father
= 6 x 1
= $6
Amount that Oscar saved
= 22.10 - 6
= $16.10
$1 = 100¢
$16.10 = 1610¢
Number of 20¢ coins |
Total value of 20¢ coins |
Number of 10¢ coins |
Total value of 10¢ coins |
Total value |
84
|
84 x 20 = 1680¢ |
0
|
0
|
1680¢
|
83
|
83 x 20 = 1660¢ |
1
|
1 x 10 = 10¢ |
1670¢
|
77 |
77 x 20 = 1540¢ |
7 |
7 x 10 = 70¢ |
1610¢
|
Amount that Oscar saved if all he saved were 20¢ coins
= 84 x 20
= 1680
Big difference between the total values of 20¢ coins and 10¢ coins
= 1680 - 1610
= 70
Small difference between the value of 20¢ coins and 10¢ coins
= 20 - 10
= 10
Number of 10¢ coins
= 70 ÷ 10
= 7
Number of 20¢ coins
= 84 - 7
= 77
Answer(s): (a) 90; (b) 77