Adam saves $5 in the 1st week and $8 in the 2nd week.
Each week, he saves $3 more than the week before.
- How much money does he save in the 9th week?
- In which week does he save $38?
(a)
Amount that Adam saves on Week 1: $5
Amount that Adam saves on Week 2: $8 = 5 + 3 = 5 + (3 x 1)
Amount that Adam saves on Week 3: $11 = 5 + 3 + 3 = 5 + (3 x 2)
Amount that Adam saves on a certain week = 5 +(3 x (Week number - 1))
Amount that Adam saves on Week 9
= 5 + 3 × (9 - 1)
= 5 + 3 × 8
= 5 + 24
= $29
(b)
5 + 3 x (Week number - 1) = 38
3 x (Week number - 5) = 38 - 5
3 x (Week number - 5) = 33
Week number - 1 = 33 ÷ 3
Week number - 1 = 11
Week number = 11 + 1
Week number = 12
Answer(s): (a) $29; (b) 12