PSLE Betty started a savings plan by putting 2 coins into a money box every day. Each coin was either a 20¢ or 50¢ coin. Her mother also put in $2 note in the box every 3 days. The total value of the savings after 138 days was $180.20.
- How many coins were there altogether?
- How many of the coins were 50¢ coins?
(a)
Total number of coins
= 2 x 138
= 276
(b)
Number of sets of 3 days
= 138 ÷ 3
= 46
Amount that her mother put in
= 46 x 2
= $92
Amount that Betty saved by herself
= 180.20 - 92
= $88.20
Number of 50¢ |
Value of 50¢ |
Number of 20¢ |
Value of 20¢ |
Total value |
276 |
276 x 0.5 = 138 |
0 |
0 |
138 |
275 |
275 x 0.5 = 137.5 |
1 |
1 x 0.2 = 0.2 |
137.7 |
Small difference
= 138 - 137.7
= 0.3
Big difference
= 138 - 88.2
= 49.8
$1 = 100¢
$0.30 = 0.30 x 100 = 30¢
$49.80 = 49.80 x 100 = 4980¢
Number of 20¢ coins
= 4980 ÷ 30
= 166
Number of 50¢ coins
= 276 - 166
= 110
Answer(s): (a) 276; (b) 110