PSLE Natalie started a savings plan by putting 2 coins into a money box every day. Each coin was either a 10¢ or 50¢ coin. Her uncle also put in $5 note in the box every 2 days. The total value of the savings after 140 days was $425.20.
- How many coins were there altogether?
- How many of the coins were 50¢ coins?
(a)
Total number of coins
= 2 x 140
= 280
(b)
Number of sets of 2 days
= 140 ÷ 2
= 70
Amount that her uncle put in
= 70 x 5
= $350
Amount that Natalie saved by herself
= 425.20 - 350
= $75.20
Number of 50¢ |
Value of 50¢ |
Number of 10¢ |
Value of 10¢ |
Total value |
280 |
280 x 0.5 = 140 |
0 |
0 |
140 |
279 |
279 x 0.5 = 139.5 |
1 |
1 x 0.1 = 0.1 |
139.6 |
Small difference
= 140 - 139.6
= 0.4
Big difference
= 140 - 75.2
= 64.8
$1 = 100¢
$0.40 = 0.40 x 100 = 40¢
$64.80 = 64.80 x 100 = 6480¢
Number of 10¢ coins
= 6480 ÷ 40
= 162
Number of 50¢ coins
= 280 - 162
= 118
Answer(s): (a) 280; (b) 118