Adam saves $3 in the 1st week and $7 in the 2nd week.
Each week, he saves $4 more than the week before.
- How much money does he save in the 8th week?
- In which week does he save $39?
(a)
Amount that Adam saves on Week 1: $3
Amount that Adam saves on Week 2: $7 = 3 + 4 = 3 + (4 x 1)
Amount that Adam saves on Week 3: $11 = 3 + 4 + 4 = 3 + (4 x 2)
Amount that Adam saves on a certain week = 3 +(4 x (Week number - 1))
Amount that Adam saves on Week 8
= 3 + 4 × (8 - 1)
= 3 + 4 × 7
= 3 + 28
= $31
(b)
3 + 4 x (Week number - 1) = 39
4 x (Week number - 3) = 39 - 3
4 x (Week number - 3) = 36
Week number - 1 = 36 ÷ 4
Week number - 1 = 9
Week number = 9 + 1
Week number = 10
Answer(s): (a) $31; (b) 10