PSLE Betty 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 $10 note in the box every 4 days. The total value of the savings after 136 days was $377.80.
- How many coins were there altogether?
- How many of the coins were 20¢ coins?
(a)
Total number of coins
= 2 x 136
= 272
(b)
Number of sets of 4 days
= 136 ÷ 4
= 34
Amount that her mother put in
= 34 x 10
= $340
Amount that Betty saved by herself
= 377.80 - 340
= $37.80
Number of 20¢ |
Value of 20¢ |
Number of 10¢ |
Value of 10¢ |
Total value |
272 |
272 x 0.2 = 54.4 |
0 |
0 |
54.4 |
271 |
271 x 0.2 = 54.2 |
1 |
1 x 0.1 = 0.1 |
54.3 |
Small difference
= 54.4 - 54.3
= 0.1
Big difference
= 54.4 - 37.8
= 16.6
$1 = 100¢
$0.10 = 0.10 x 100 = 10¢
$16.60 = 16.60 x 100 = 1660¢
Number of 10¢ coins
= 1660 ÷ 10
= 166
Number of 20¢ coins
= 272 - 166
= 106
Answer(s): (a) 272; (b) 106