Cathy was saving money to buy pens. She saved $5 every 8 days. After saving for 40 days, she went to buy pens that were on sale.

1. What was the most number of pens she could buy?
2. Cathy wanted to buy 28 pens. How much more did she need to save?

(a)
Number of sets of 8 days
= 40 ÷ 8
= 5

Amount that Cathy saved in 40 days
= 5 x 5
= $25

Maximum number of sets of 6 pens that Cathy could buy 
= 25 ÷ 9
= 2 r $7

Remaining amount left after buying sets of 6 pens = $7

Maximum number of sets of 3 pens that Cathy could buy with $7
= 7 ÷ 5
= 1 r $2 

Remaining amount left after buying sets of 3 pens = $2

Maximum number of pens that Cathy could buy with $2 
= 2 ÷ 2
= 1

Most number of pens that Cathy could buy
= 2 x 6 + 1 x 3 + 1
= 12 + 3 + 1
= 16

(b)
Number of sets of 6 pens that Cathy could buy
= 28 ÷ 6
= 4 r 4

Number of sets of 3 pens that Cathy could buy
= 4 ÷ 3
= 1 r 1

Number of individual pens that Cathy could buy = 1

Amount that Cathy needed to buy 28 pens
= 4 x 9 + 1 x 5 + 2
= 36 + 5 + 2
= $43

Amount that Cathy needed to save more
= 43 - 25
= $18

Answer(s): (a) 16; (b) $18