The amount donated starts at 10, then grows by 6 each week. So, the donated amounts are
10,16,22,28,...
So, the donated amount for the nth week is an arithmetic progression with
a = 10, d=6
The total donations in 20 weeks is thus
S20 = 20/2 (2*10 + 19*6) = 1340
Add that to the initial 300 books, and you have 1640, as you said.
The book total in week n is
300 + 10 + (n-1)*6 = 304+6n
A library opens with a collection of 300 books. During the first week after
the opening, an additional ten books are donated to the library’s
collection. In each subsequent week, six more books are donated to the
library’s collection than were donated in the previous week. Work out how
many books are in the library’s collection after twenty weeks.
310, 316, 328, 346, 370....
I have the answer is 1640 just not sure how to write it as an nth term?
1 answer
1 answer