Emma was saving money to buy pens. She saved $4 every 3 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. Emma wanted to buy 24 pens. How much more did she need to save?

(a)
Number of sets of 3 days
= 24 ÷ 3
= 8

Amount that Emma saved in 24 days
= 8 x 4
= $32

Maximum number of sets of 5 pens that Emma could buy 
= 32 ÷ 11
= 2 r $10

Remaining amount left after buying sets of 5 pens = $10

Maximum number of sets of 3 pens that Emma could buy with $10
= 10 ÷ 7
= 1 r $3 

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

Maximum number of pens that Emma could buy with $3 
= 3 ÷ 3
= 1

Most number of pens that Emma could buy
= 2 x 5 + 1 x 3 + 1
= 10 + 3 + 1
= 14

(b)
Number of sets of 5 pens that Emma could buy
= 24 ÷ 5
= 4 r 4

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

Number of individual pens that Emma could buy = 1

Amount that Emma needed to buy 24 pens
= 4 x 11 + 1 x 7 + 3
= 44 + 7 + 3
= $54

Amount that Emma needed to save more
= 54 - 32
= $22

Answer(s): (a) 14; (b) $22