PSLE In a shop, candles are sold only in boxes. A box of 7 short candles costs $3.70 and a box of 5 long candles costs $5.50.
- Rael wants 17 short candles and 3 long candles for his lanterns. What is the least amount of money that Rael will need to spend on the candles?
- Fanny bought 4 more long candles than short candles from the shop. The total number of candles she bought was fewer than 50. How much did Fanny spend on the candles altogether?
(a)
Number of sets of 7 short candles
= 17 ÷ 7
= 2 r 3
Number of boxes of short candles that Rael needs to buy
= 2 + 1
= 3
Amount that Rael needs to spend on short candles
= 3 x 3.70
= $11.10
Least amount that Rael will need to spend
= 11.10 + 5.50
= $16.60
(b)
Packets of
long candles
|
Number of
long candles
(x5) |
Packets of
short candles
|
Number of
short candles
(x7) |
Total
|
Difference
|
Check
|
| 7 |
35 |
2 |
14 |
49 |
35 - 14 =
21 |
x |
| 6 |
30 |
2 |
14 |
44 |
30 - 14 =
16 |
x |
| 5 |
25 |
3 |
21 |
46 |
25 - 21 =
4 |
✓ |
To know the number of packets of long candles and short candles, we list the multiplies of 5 and 7.
We use systematic listing to find the difference between the number of long candles and short candles so that we can find the right combination that will result in having 4 more long candles.
We also check if the total number of candles must be less than 50.
Multiples of 5: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50
Multiples of 7: 7, 14, 21, 28, 35, 42, 49
Number of packets of long candles = 5
Cost of long candles
= 5 x 5.50
= $27.50
Cost of short candles
= 3 x 3.70
= $11.10
Total amount that Fanny spent on the candles
= 27.50 + 11.10
= $38.60
Answer(s): (a) $16.60; (b) $38.60
