PSLE Emily 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 3 days. The total value of the savings after 105 days was $421.40.
- How many coins were there altogether?
- How many of the coins were 50¢ coins?
(a)
Total number of coins
= 2 x 105
= 210
(b)
Number of sets of 3 days
= 105 ÷ 3
= 35
Amount that her aunt put in
= 35 x 10
= $350
Amount that Emily saved by herself
= 421.40 - 350
= $71.40
Number of 50¢ |
Value of 50¢ |
Number of 10¢ |
Value of 10¢ |
Total value |
210 |
210 x 0.5 = 105 |
0 |
0 |
105 |
209 |
209 x 0.5 = 104.5 |
1 |
1 x 0.1 = 0.1 |
104.6 |
Small difference
= 105 - 104.6
= 0.4
Big difference
= 105 - 71.4
= 33.6
$1 = 100¢
$0.40 = 0.40 x 100 = 40¢
$33.60 = 33.60 x 100 = 3360¢
Number of 10¢ coins
= 3360 ÷ 40
= 84
Number of 50¢ coins
= 210 - 84
= 126
Answer(s): (a) 210; (b) 126