PSLE Xuan started a savings plan by putting 2 coins into a money box every day. Each coin was either a 10¢ or 20¢ coin. Her uncle also put in $2 note in the box every 2 days. The total value of the savings after 102 days was $135.50.
- How many coins were there altogether?
- How many of the coins were 20¢ coins?
(a)
Total number of coins
= 2 x 102
= 204
(b)
Number of sets of 2 days
= 102 ÷ 2
= 51
Amount that her uncle put in
= 51 x 2
= $102
Amount that Xuan saved by herself
= 135.50 - 102
= $33.50
Number of 20¢ |
Value of 20¢ |
Number of 10¢ |
Value of 10¢ |
Total value |
204 |
204 x 0.2 = 40.8 |
0 |
0 |
40.8 |
203 |
203 x 0.2 = 40.6 |
1 |
1 x 0.1 = 0.1 |
40.7 |
Small difference
= 40.8 - 40.7
= 0.1
Big difference
= 40.8 - 33.5
= 7.3
$1 = 100¢
$0.10 = 0.10 x 100 = 10¢
$7.30 = 7.30 x 100 = 730¢
Number of 10¢ coins
= 730 ÷ 10
= 73
Number of 20¢ coins
= 204 - 73
= 131
Answer(s): (a) 204; (b) 131