Adam saves $3 in the 1st week and $8 in the 2nd week.
Each week, he saves $5 more than the week before.
- How much money does he save in the 6th week?
- In which week does he save $18?
(a)
Amount that Adam saves on Week 1: $3
Amount that Adam saves on Week 2: $8 = 3 + 5 = 3 + (5 x 1)
Amount that Adam saves on Week 3: $13 = 3 + 5 + 5 = 3 + (5 x 2)
Amount that Adam saves on a certain week = 3 +(5 x (Week number - 1))
Amount that Adam saves on Week 6
= 3 + 5 × (6 - 1)
= 3 + 5 × 5
= 3 + 25
= $28
(b)
3 + 5 x (Week number - 1) = 18
5 x (Week number - 3) = 18 - 3
5 x (Week number - 3) = 15
Week number - 1 = 15 ÷ 5
Week number - 1 = 3
Week number = 3 + 1
Week number = 4
Answer(s): (a) $28; (b) 4