PSLE Mary 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 $2 note in the box every 5 days. The total value of the savings after 110 days was $124.80.
- How many coins were there altogether?
- How many of the coins were 50¢ coins?
(a)
Total number of coins
= 2 x 110
= 220
(b)
Number of sets of 5 days
= 110 ÷ 5
= 22
Amount that her uncle put in
= 22 x 2
= $44
Amount that Mary saved by herself
= 124.80 - 44
= $80.80
Number of 50¢ |
Value of 50¢ |
Number of 10¢ |
Value of 10¢ |
Total value |
220 |
220 x 0.5 = 110 |
0 |
0 |
110 |
219 |
219 x 0.5 = 109.5 |
1 |
1 x 0.1 = 0.1 |
109.6 |
Small difference
= 110 - 109.6
= 0.4
Big difference
= 110 - 80.8
= 29.2
$1 = 100¢
$0.40 = 0.40 x 100 = 40¢
$29.20 = 29.20 x 100 = 2920¢
Number of 10¢ coins
= 2920 ÷ 40
= 73
Number of 50¢ coins
= 220 - 73
= 147
Answer(s): (a) 220; (b) 147