Adam saves $4 in the 1st week and $7 in the 2nd week.
Each week, he saves $3 more than the week before.
- How much money does he save in the 6th week?
- In which week does he save $58?
(a)
Amount that Adam saves on Week 1: $4
Amount that Adam saves on Week 2: $7 = 4 + 3 = 4 + (3 x 1)
Amount that Adam saves on Week 3: $10 = 4 + 3 + 3 = 4 + (3 x 2)
Amount that Adam saves on a certain week = 4 +(3 x (Week number - 1))
Amount that Adam saves on Week 6
= 4 + 3 × (6 - 1)
= 4 + 3 × 5
= 4 + 15
= $19
(b)
4 + 3 x (Week number - 1) = 58
3 x (Week number - 4) = 58 - 4
3 x (Week number - 4) = 54
Week number - 1 = 54 ÷ 3
Week number - 1 = 18
Week number = 18 + 1
Week number = 19
Answer(s): (a) $19; (b) 19