Riordan received $3 from his mother in the 1st week of school and $5 in the 2nd week. Each week, he receives $2 more than the week before.
- How much money did he received in the 19th week?
- In which week did he receive $21?
(a)
Amount that Riordan received on 1st Week = $3
Amount that Riordan received on 2nd Week = $18
Formula:
Amount received each week = 3 + (Week number - 1) x $2
Amount received on Week 19
= 3 + (19 - 1) x 2
= 3 + 18 x 2
= 3 + 36
= $39
(b)
Week number that Riordan received $21
= [(21 - 3) ÷ 2] + 1
= (18 ÷ 2) + 1
= 9 + 1
= 10
Answer(s): (a) $39; (b) 10