PSLE Tina 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 $2 note in the box every 4 days. The total value of the savings after 140 days was $140.40.
- 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 4 days
= 140 ÷ 4
= 35
Amount that her mother put in
= 35 x 2
= $70
Amount that Tina saved by herself
= 140.40 - 70
= $70.40
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 - 70.4
= 69.6
$1 = 100¢
$0.40 = 0.40 x 100 = 40¢
$69.60 = 69.60 x 100 = 6960¢
Number of 10¢ coins
= 6960 ÷ 40
= 174
Number of 50¢ coins
= 280 - 174
= 106
Answer(s): (a) 280; (b) 106