Zara was saving money to buy pens. She saved $7 every 6 days. After saving for 24 days, she went to buy pens that were on sale.

1. What was the most number of pens she could buy?
2. Zara wanted to buy 33 pens. How much more did she need to save?

(a)
Number of sets of 6 days
= 24 ÷ 6
= 4

Amount that Zara saved in 24 days
= 4 x 7
= $28

Maximum number of sets of 9 pens that Zara could buy 
= 28 ÷ 10
= 2 r $8

Remaining amount left after buying sets of 9 pens = $8

Maximum number of sets of 5 pens that Zara could buy with $8
= 8 ÷ 6
= 1 r $2 

Remaining amount left after buying sets of 5 pens = $2

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

Most number of pens that Zara could buy
= 2 x 9 + 1 x 5 + 1
= 18 + 5 + 1
= 24

(b)
Number of sets of 9 pens that Zara could buy
= 33 ÷ 9
= 3 r 6

Number of sets of 5 pens that Zara could buy
= 6 ÷ 5
= 1 r 1

Number of individual pens that Zara could buy = 1

Amount that Zara needed to buy 33 pens
= 3 x 10 + 1 x 6 + 2
= 30 + 6 + 2
= $38

Amount that Zara needed to save more
= 38 - 28
= $10

Answer(s): (a) 24; (b) $10