Adam saves $1 in the 1st week and $5 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 $29?
(a)
Amount that Adam saves on Week 1: $1
Amount that Adam saves on Week 2: $5 = 1 + 4 = 1 + (4 x 1)
Amount that Adam saves on Week 3: $9 = 1 + 4 + 4 = 1 + (4 x 2)
Amount that Adam saves on a certain week = 1 +(4 x (Week number - 1))
Amount that Adam saves on Week 10
= 1 + 4 × (10 - 1)
= 1 + 4 × 9
= 1 + 36
= $37
(b)
1 + 4 x (Week number - 1) = 29
4 x (Week number - 1) = 29 - 1
4 x (Week number - 1) = 28
Week number - 1 = 28 ÷ 4
Week number - 1 = 7
Week number = 7 + 1
Week number = 8
Answer(s): (a) $37; (b) 8