Adam saves $4 in the 1st week and $8 in the 2nd week.
Each week, he saves $4 more than the week before.
- How much money does he save in the 10th week?
- In which week does he save $36?
(a)
Amount that Adam saves on Week 1: $4
Amount that Adam saves on Week 2: $8 = 4 + 4 = 4 + (4 x 1)
Amount that Adam saves on Week 3: $12 = 4 + 4 + 4 = 4 + (4 x 2)
Amount that Adam saves on a certain week = 4 +(4 x (Week number - 1))
Amount that Adam saves on Week 10
= 4 + 4 × (10 - 1)
= 4 + 4 × 9
= 4 + 36
= $40
(b)
4 + 4 x (Week number - 1) = 36
4 x (Week number - 4) = 36 - 4
4 x (Week number - 4) = 32
Week number - 1 = 32 ÷ 4
Week number - 1 = 8
Week number = 8 + 1
Week number = 9
Answer(s): (a) $40; (b) 9