Adam saves $1 in the 1st week and $4 in the 2nd week.
Each week, he saves $3 more than the week before.
- How much money does he save in the 10th week?
- In which week does he save $55?
(a)
Amount that Adam saves on Week 1: $1
Amount that Adam saves on Week 2: $4 = 1 + 3 = 1 + (3 x 1)
Amount that Adam saves on Week 3: $7 = 1 + 3 + 3 = 1 + (3 x 2)
Amount that Adam saves on a certain week = 1 +(3 x (Week number - 1))
Amount that Adam saves on Week 10
= 1 + 3 × (10 - 1)
= 1 + 3 × 9
= 1 + 27
= $28
(b)
1 + 3 x (Week number - 1) = 55
3 x (Week number - 1) = 55 - 1
3 x (Week number - 1) = 54
Week number - 1 = 54 ÷ 3
Week number - 1 = 18
Week number = 18 + 1
Week number = 19
Answer(s): (a) $28; (b) 19