PSLE Gwen started a savings plan by putting 2 coins into a money box every day. Each coin was either a 10¢ or 20¢ coin. Her aunt also put in $2 note in the box every 4 days. The total value of the savings after 128 days was $101.30.
- How many coins were there altogether?
- How many of the coins were 20¢ coins?
(a)
Total number of coins
= 2 x 128
= 256
(b)
Number of sets of 4 days
= 128 ÷ 4
= 32
Amount that her aunt put in
= 32 x 2
= $64
Amount that Gwen saved by herself
= 101.30 - 64
= $37.30
Number of 20¢ |
Value of 20¢ |
Number of 10¢ |
Value of 10¢ |
Total value |
256 |
256 x 0.2 = 51.2 |
0 |
0 |
51.2 |
255 |
255 x 0.2 = 51 |
1 |
1 x 0.1 = 0.1 |
51.1 |
Small difference
= 51.2 - 51.1
= 0.1
Big difference
= 51.2 - 37.3
= 13.9
$1 = 100¢
$0.10 = 0.10 x 100 = 10¢
$13.90 = 13.90 x 100 = 1390¢
Number of 10¢ coins
= 1390 ÷ 10
= 139
Number of 20¢ coins
= 256 - 139
= 117
Answer(s): (a) 256; (b) 117