PSLE Shiyun started a savings plan by putting 2 coins into a money box every day. Each coin was either a 20¢ or 50¢ coin. Her aunt also put in $10 note in the box every 2 days. The total value of the savings after 120 days was $686.40.
- How many coins were there altogether?
- How many of the coins were 50¢ coins?
(a)
Total number of coins
= 2 x 120
= 240
(b)
Number of sets of 2 days
= 120 ÷ 2
= 60
Amount that her aunt put in
= 60 x 10
= $600
Amount that Shiyun saved by herself
= 686.40 - 600
= $86.40
Number of 50¢ |
Value of 50¢ |
Number of 20¢ |
Value of 20¢ |
Total value |
240 |
240 x 0.5 = 120 |
0 |
0 |
120 |
239 |
239 x 0.5 = 119.5 |
1 |
1 x 0.2 = 0.2 |
119.7 |
Small difference
= 120 - 119.7
= 0.3
Big difference
= 120 - 86.4
= 33.6
$1 = 100¢
$0.30 = 0.30 x 100 = 30¢
$33.60 = 33.60 x 100 = 3360¢
Number of 20¢ coins
= 3360 ÷ 30
= 112
Number of 50¢ coins
= 240 - 112
= 128
Answer(s): (a) 240; (b) 128