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 uncle also put in $10 note in the box every 5 days. The total value of the savings after 140 days was $318.60.
- How many coins were there altogether?
- How many of the coins were 20¢ coins?
(a)
Total number of coins
= 2 x 140
= 280
(b)
Number of sets of 5 days
= 140 ÷ 5
= 28
Amount that her uncle put in
= 28 x 10
= $280
Amount that Jean saved by herself
= 318.60 - 280
= $38.60
Number of 20¢ |
Value of 20¢ |
Number of 10¢ |
Value of 10¢ |
Total value |
280 |
280 x 0.2 = 56 |
0 |
0 |
56 |
279 |
279 x 0.2 = 55.8 |
1 |
1 x 0.1 = 0.1 |
55.9 |
Small difference
= 56 - 55.9
= 0.1
Big difference
= 56 - 38.6
= 17.4
$1 = 100¢
$0.10 = 0.10 x 100 = 10¢
$17.40 = 17.40 x 100 = 1740¢
Number of 10¢ coins
= 1740 ÷ 10
= 174
Number of 20¢ coins
= 280 - 174
= 106
Answer(s): (a) 280; (b) 106