Adam saves $1 in the 1st week and $6 in the 2nd week.
Each week, he saves $5 more than the week before.
- How much money does he save in the 9th week?
- In which week does he save $31?
(a)
Amount that Adam saves on Week 1: $1
Amount that Adam saves on Week 2: $6 = 1 + 5 = 1 + (5 x 1)
Amount that Adam saves on Week 3: $11 = 1 + 5 + 5 = 1 + (5 x 2)
Amount that Adam saves on a certain week = 1 +(5 x (Week number - 1))
Amount that Adam saves on Week 9
= 1 + 5 × (9 - 1)
= 1 + 5 × 8
= 1 + 40
= $41
(b)
1 + 5 x (Week number - 1) = 31
5 x (Week number - 1) = 31 - 1
5 x (Week number - 1) = 30
Week number - 1 = 30 ÷ 5
Week number - 1 = 6
Week number = 6 + 1
Week number = 7
Answer(s): (a) $41; (b) 7