PSLE Winnie started a savings plan by putting 2 coins into a money box every day. Each coin was either a 10¢ or 20¢ coin. Her father also put in $10 note in the box every 3 days. The total value of the savings after 129 days was $466.30.
- How many coins were there altogether?
- How many of the coins were 20¢ coins?
(a)
Total number of coins
= 2 x 129
= 258
(b)
Number of sets of 3 days
= 129 ÷ 3
= 43
Amount that her father put in
= 43 x 10
= $430
Amount that Winnie saved by herself
= 466.30 - 430
= $36.30
Number of 20¢ |
Value of 20¢ |
Number of 10¢ |
Value of 10¢ |
Total value |
258 |
258 x 0.2 = 51.6 |
0 |
0 |
51.6 |
257 |
257 x 0.2 = 51.4 |
1 |
1 x 0.1 = 0.1 |
51.5 |
Small difference
= 51.6 - 51.5
= 0.1
Big difference
= 51.6 - 36.3
= 15.3
$1 = 100¢
$0.10 = 0.10 x 100 = 10¢
$15.30 = 15.30 x 100 = 1530¢
Number of 10¢ coins
= 1530 ÷ 10
= 153
Number of 20¢ coins
= 258 - 153
= 105
Answer(s): (a) 258; (b) 105