Adam saves $3 in the 1st week and $6 in the 2nd week.
Each week, he saves $3 more than the week before.
- How much money does he save in the 5th week?
- In which week does he save $42?
(a)
Amount that Adam saves on Week 1: $3
Amount that Adam saves on Week 2: $6 = 3 + 3 = 3 + (3 x 1)
Amount that Adam saves on Week 3: $9 = 3 + 3 + 3 = 3 + (3 x 2)
Amount that Adam saves on a certain week = 3 +(3 x (Week number - 1))
Amount that Adam saves on Week 5
= 3 + 3 × (5 - 1)
= 3 + 3 × 4
= 3 + 12
= $15
(b)
3 + 3 x (Week number - 1) = 42
3 x (Week number - 3) = 42 - 3
3 x (Week number - 3) = 39
Week number - 1 = 39 ÷ 3
Week number - 1 = 13
Week number = 13 + 1
Week number = 14
Answer(s): (a) $15; (b) 14