PSLE Mary started a savings plan by putting 2 coins into a money box every day. Each coin was either a 20¢ or 50¢ coin. Her mother also put in $2 note in the box every 5 days. The total value of the savings after 100 days was $124.40.
- How many coins were there altogether?
- How many of the coins were 50¢ coins?
(a)
Total number of coins
= 2 x 100
= 200
(b)
Number of sets of 5 days
= 100 ÷ 5
= 20
Amount that her mother put in
= 20 x 2
= $40
Amount that Mary saved by herself
= 124.40 - 40
= $84.40
Number of 50¢ |
Value of 50¢ |
Number of 20¢ |
Value of 20¢ |
Total value |
200 |
200 x 0.5 = 100 |
0 |
0 |
100 |
199 |
199 x 0.5 = 99.5 |
1 |
1 x 0.2 = 0.2 |
99.7 |
Small difference
= 100 - 99.7
= 0.3
Big difference
= 100 - 84.4
= 15.6
$1 = 100¢
$0.30 = 0.30 x 100 = 30¢
$15.60 = 15.60 x 100 = 1560¢
Number of 20¢ coins
= 1560 ÷ 30
= 52
Number of 50¢ coins
= 200 - 52
= 148
Answer(s): (a) 200; (b) 148