Xuan was saving money to buy pens. She saved $9 every 5 days. After saving for 30 days, she went to buy pens that were on sale.
- What was the most number of pens she could buy?
- Xuan wanted to buy 51 pens. How much more did she need to save?
(a)
Number of sets of 5 days
= 30 ÷ 5
= 6
Amount that Xuan saved in 30 days
= 6 x 9
= $54
Maximum number of sets of 9 pens that Xuan could buy
= 54 ÷ 11
= 4 r $10
Remaining amount left after buying sets of 9 pens = $10
Maximum number of sets of 5 pens that Xuan could buy with $10
= 10 ÷ 7
= 1 r $3
Remaining amount left after buying sets of 5 pens = $3
Maximum number of pens that Xuan could buy with $3
= 3 ÷ 3
= 1
Most number of pens that Xuan could buy
= 4 x 9 + 1 x 5 + 1
= 36 + 5 + 1
= 42
(b)
Number of sets of 9 pens that Xuan could buy
= 51 ÷ 9
= 5 r 6
Number of sets of 5 pens that Xuan could buy
= 6 ÷ 5
= 1 r 1
Number of individual pens that Xuan could buy = 1
Amount that Xuan needed to buy 51 pens
= 5 x 11 + 1 x 7 + 3
= 55 + 7 + 3
= $65
Amount that Xuan needed to save more
= 65 - 54
= $11
Answer(s): (a) 42; (b) $11