A boy was building up his collection of marbles.He decided to increase his collection by 12 a week.After 13 weeks he had 161 marbles.

Question

(i) How many marbles did he have after 4 weeks?

(ii) After how many complete weeks will he reach his target of 809 marbles?

Answer 1

161 = 13*12 + 5

(i)
after 4 weeks he had 5 + 4*12 = 53

(ii)
n/2 (5+12(n-1)) = 809
n ≈ 11.7

So, after 12 weeks he had more than 809 marbles