Adam saves $5 in the 1st week and $10 in the 2nd week.
Each week, he saves $5 more than the week before.
- How much money does he save in the 5th week?
- In which week does he save $40?
(a)
Amount that Adam saves on Week 1: $5
Amount that Adam saves on Week 2: $10 = 5 + 5 = 5 + (5 x 1)
Amount that Adam saves on Week 3: $15 = 5 + 5 + 5 = 5 + (5 x 2)
Amount that Adam saves on a certain week = 5 +(5 x (Week number - 1))
Amount that Adam saves on Week 5
= 5 + 5 × (5 - 1)
= 5 + 5 × 4
= 5 + 20
= $25
(b)
5 + 5 x (Week number - 1) = 40
5 x (Week number - 5) = 40 - 5
5 x (Week number - 5) = 35
Week number - 1 = 35 ÷ 5
Week number - 1 = 7
Week number = 7 + 1
Week number = 8
Answer(s): (a) $25; (b) 8