PSLE Diana started a savings plan by putting 2 coins into a money box every day. Each coin was either a 10¢ or 20¢ coin. Her mother also put in $2 note in the box every 3 days. The total value of the savings after 117 days was $113.40.
- How many coins were there altogether?
- How many of the coins were 20¢ coins?
(a)
Total number of coins
= 2 x 117
= 234
(b)
Number of sets of 3 days
= 117 ÷ 3
= 39
Amount that her mother put in
= 39 x 2
= $78
Amount that Diana saved by herself
= 113.40 - 78
= $35.40
Number of 20¢ |
Value of 20¢ |
Number of 10¢ |
Value of 10¢ |
Total value |
234 |
234 x 0.2 = 46.8 |
0 |
0 |
46.8 |
233 |
233 x 0.2 = 46.6 |
1 |
1 x 0.1 = 0.1 |
46.7 |
Small difference
= 46.8 - 46.7
= 0.1
Big difference
= 46.8 - 35.4
= 11.4
$1 = 100¢
$0.10 = 0.10 x 100 = 10¢
$11.40 = 11.40 x 100 = 1140¢
Number of 10¢ coins
= 1140 ÷ 10
= 114
Number of 20¢ coins
= 234 - 114
= 120
Answer(s): (a) 234; (b) 120