PSLE Shiyun started a savings plan by putting 2 coins into a money box every day. Each coin was either a 10¢ or 50¢ coin. Her father also put in $2 note in the box every 4 days. The total value of the savings after 120 days was $132.80.
- 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 4 days
= 120 ÷ 4
= 30
Amount that her father put in
= 30 x 2
= $60
Amount that Shiyun saved by herself
= 132.80 - 60
= $72.80
Number of 50¢ |
Value of 50¢ |
Number of 10¢ |
Value of 10¢ |
Total value |
240 |
240 x 0.5 = 120 |
0 |
0 |
120 |
239 |
239 x 0.5 = 119.5 |
1 |
1 x 0.1 = 0.1 |
119.6 |
Small difference
= 120 - 119.6
= 0.4
Big difference
= 120 - 72.8
= 47.2
$1 = 100¢
$0.40 = 0.40 x 100 = 40¢
$47.20 = 47.20 x 100 = 4720¢
Number of 10¢ coins
= 4720 ÷ 40
= 118
Number of 50¢ coins
= 240 - 118
= 122
Answer(s): (a) 240; (b) 122