Reggie 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 77 days was $31.90.
- How many coins were there altogether?
- How many of the coins were 20¢ coins?
Total nuber of coins that his father put in
= 77 ÷ 7
= 11
Total number of coins that Reggie saved
= 2 x 77 = 154 Total number of coins
= 11 + 154
= 165
(b)
Amount contributed by his father
= 11 x 1
= $11
Amount that Reggie saved
= 31.90 - 11
= $20.90
$1 = 100¢
$20.90 = 2090¢
Number of
20¢ coins |
Total value
of 20¢ coins |
Number of
10¢ coins |
Total value
of 10¢ coins |
Total value |
154
|
154 x 20
= 3080¢ |
0
|
0
|
3080¢
|
153
|
153 x 20
= 3060¢ |
1
|
1 x 10 =
10¢ |
3070¢
|
| 55 |
55 x 20
= 1100¢ |
99 |
99 x 10 =
990¢ |
2090¢
|
Amount that Reggie saved if all he saved were 20¢ coins
= 154 x 20
= 3080
Big difference between the total values of 20¢ coins and 10¢ coins
= 3080 - 2090
= 990
Small difference between the value of 20¢ coins and 10¢ coins
= 20 - 10
= 10
Number of 10¢ coins
= 990 ÷ 10
= 99
Number of 20¢ coins
= 154 - 99
= 55
Answer(s): (a) 165; (b) 55
