PSLE Jean started a savings plan by putting 2 coins into a money box every day. Each coin was either a 10¢ or 20¢ coin. Her aunt also put in $5 note in the box every 2 days. The total value of the savings after 100 days was $282.80.
- How many coins were there altogether?
- How many of the coins were 20¢ coins?
(a)
Total number of coins
= 2 x 100
= 200
(b)
Number of sets of 2 days
= 100 ÷ 2
= 50
Amount that her aunt put in
= 50 x 5
= $250
Amount that Jean saved by herself
= 282.80 - 250
= $32.80
Number of 20¢ |
Value of 20¢ |
Number of 10¢ |
Value of 10¢ |
Total value |
200 |
200 x 0.2 = 40 |
0 |
0 |
40 |
199 |
199 x 0.2 = 39.8 |
1 |
1 x 0.1 = 0.1 |
39.9 |
Small difference
= 40 - 39.9
= 0.1
Big difference
= 40 - 32.8
= 7.2
$1 = 100¢
$0.10 = 0.10 x 100 = 10¢
$7.20 = 7.20 x 100 = 720¢
Number of 10¢ coins
= 720 ÷ 10
= 72
Number of 20¢ coins
= 200 - 72
= 128
Answer(s): (a) 200; (b) 128