Adam saves $4 in the 1st week and $6 in the 2nd week.
Each week, he saves $2 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: $4
Amount that Adam saves on Week 2: $6 = 4 + 2 = 4 + (2 x 1)
Amount that Adam saves on Week 3: $8 = 4 + 2 + 2 = 4 + (2 x 2)
Amount that Adam saves on a certain week = 4 +(2 x (Week number - 1))
Amount that Adam saves on Week 9
= 4 + 2 × (9 - 1)
= 4 + 2 × 8
= 4 + 16
= $20
(b)
4 + 2 x (Week number - 1) = 58
2 x (Week number - 4) = 58 - 4
2 x (Week number - 4) = 54
Week number - 1 = 54 ÷ 2
Week number - 1 = 27
Week number = 27 + 1
Week number = 28
Answer(s): (a) $20; (b) 28