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 4th week?
- In which week does he save $40?
(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 4
= 4 + 4 × (4 - 1)
= 4 + 4 × 3
= 4 + 12
= $16
(b)
4 + 4 x (Week number - 1) = 40
4 x (Week number - 4) = 40 - 4
4 x (Week number - 4) = 36
Week number - 1 = 36 ÷ 4
Week number - 1 = 9
Week number = 9 + 1
Week number = 10
Answer(s): (a) $16; (b) 10