Adam saves $3 in the 1st week and $8 in the 2nd week.
Each week, he saves $5 more than the week before.
- How much money does he save in the 9th week?
- In which week does he save $58?
(a)
Amount that Adam saves on Week 1: $3
Amount that Adam saves on Week 2: $8 = 3 + 5 = 3 + (5 x 1)
Amount that Adam saves on Week 3: $13 = 3 + 5 + 5 = 3 + (5 x 2)
Amount that Adam saves on a certain week = 3 +(5 x (Week number - 1))
Amount that Adam saves on Week 9
= 3 + 5 × (9 - 1)
= 3 + 5 × 8
= 3 + 40
= $43
(b)
3 + 5 x (Week number - 1) = 58
5 x (Week number - 3) = 58 - 3
5 x (Week number - 3) = 55
Week number - 1 = 55 ÷ 5
Week number - 1 = 11
Week number = 11 + 1
Week number = 12
Answer(s): (a) $43; (b) 12