PSLE Opal 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 $10 note in the box every 5 days. The total value of the savings after 170 days was $414.40.
- How many coins were there altogether?
- How many of the coins were 50¢ coins?
(a)
Total number of coins
= 2 x 170
= 340
(b)
Number of sets of 5 days
= 170 ÷ 5
= 34
Amount that her uncle put in
= 34 x 10
= $340
Amount that Opal saved by herself
= 414.40 - 340
= $74.40
Number of 50¢ |
Value of 50¢ |
Number of 10¢ |
Value of 10¢ |
Total value |
340 |
340 x 0.5 = 170 |
0 |
0 |
170 |
339 |
339 x 0.5 = 169.5 |
1 |
1 x 0.1 = 0.1 |
169.6 |
Small difference
= 170 - 169.6
= 0.4
Big difference
= 170 - 74.4
= 95.6
$1 = 100¢
$0.40 = 0.40 x 100 = 40¢
$95.60 = 95.60 x 100 = 9560¢
Number of 10¢ coins
= 9560 ÷ 40
= 239
Number of 50¢ coins
= 340 - 239
= 101
Answer(s): (a) 340; (b) 101