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 8th week?
- In which week does he save $25?
(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 8
= 1 + 4 × (8 - 1)
= 1 + 4 × 7
= 1 + 28
= $29
(b)
1 + 4 x (Week number - 1) = 25
4 x (Week number - 1) = 25 - 1
4 x (Week number - 1) = 24
Week number - 1 = 24 ÷ 4
Week number - 1 = 6
Week number = 6 + 1
Week number = 7
Answer(s): (a) $29; (b) 7