PSLE Fanny started a savings plan by putting 2 coins into a money box every day. Each coin was either a 10¢ or 50¢ coin. Her mother also put in $10 note in the box every 4 days. The total value of the savings after 168 days was $510.80.
- How many coins were there altogether?
- How many of the coins were 50¢ coins?
(a)
Total number of coins
= 2 x 168
= 336
(b)
Number of sets of 4 days
= 168 ÷ 4
= 42
Amount that her mother put in
= 42 x 10
= $420
Amount that Fanny saved by herself
= 510.80 - 420
= $90.80
Number of 50¢ |
Value of 50¢ |
Number of 10¢ |
Value of 10¢ |
Total value |
336 |
336 x 0.5 = 168 |
0 |
0 |
168 |
335 |
335 x 0.5 = 167.5 |
1 |
1 x 0.1 = 0.1 |
167.6 |
Small difference
= 168 - 167.6
= 0.4
Big difference
= 168 - 90.8
= 77.2
$1 = 100¢
$0.40 = 0.40 x 100 = 40¢
$77.20 = 77.20 x 100 = 7720¢
Number of 10¢ coins
= 7720 ÷ 40
= 193
Number of 50¢ coins
= 336 - 193
= 143
Answer(s): (a) 336; (b) 143