PSLE Betty started a savings plan by putting 2 coins into a money box every day. Each coin was either a 10¢ or 50¢ coin. Her aunt also put in $10 note in the box every 2 days. The total value of the savings after 160 days was $890.40.
- How many coins were there altogether?
- How many of the coins were 50¢ coins?
(a)
Total number of coins
= 2 x 160
= 320
(b)
Number of sets of 2 days
= 160 ÷ 2
= 80
Amount that her aunt put in
= 80 x 10
= $800
Amount that Betty saved by herself
= 890.40 - 800
= $90.40
Number of 50¢ |
Value of 50¢ |
Number of 10¢ |
Value of 10¢ |
Total value |
320 |
320 x 0.5 = 160 |
0 |
0 |
160 |
319 |
319 x 0.5 = 159.5 |
1 |
1 x 0.1 = 0.1 |
159.6 |
Small difference
= 160 - 159.6
= 0.4
Big difference
= 160 - 90.4
= 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
= 320 - 174
= 146
Answer(s): (a) 320; (b) 146