Fiona was saving money to buy pens. She saved $3 every 5 days. After saving for 50 days, she went to buy pens that were on sale.

1. What was the most number of pens she could buy?
2. Fiona wanted to buy 32 pens. How much more did she need to save?

(a)
Number of sets of 5 days
= 50 ÷ 5
= 10

Amount that Fiona saved in 50 days
= 10 x 3
= $30

Maximum number of sets of 7 pens that Fiona could buy 
= 30 ÷ 8
= 3 r $6

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

Maximum number of sets of 3 pens that Fiona could buy with $6
= 6 ÷ 4
= 1 r $2 

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

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

Most number of pens that Fiona could buy
= 3 x 7 + 1 x 3 + 1
= 21 + 3 + 1
= 25

(b)
Number of sets of 7 pens that Fiona could buy
= 32 ÷ 7
= 4 r 4

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

Number of individual pens that Fiona could buy = 1

Amount that Fiona needed to buy 32 pens
= 4 x 8 + 1 x 4 + 2
= 32 + 4 + 2
= $38

Amount that Fiona needed to save more
= 38 - 30
= $8

Answer(s): (a) 25; (b) $8