Solve the problem.
-The number of birds born each year at the local zoo forms a sequence whose general term is $a _ { n } = ( n + 9 ) ( n - 1 )$. Find the number of birds born in the fourth year, and find the total number of birds born in the first four years.
A) 39 birds; 84 birds
B) 24 birds; 45 birds
C) 39 birds; 74 birds
D) 24 birds; 35 birds

Question

Quizplus · Accepted Answer

In the fourth year, $a_4 = (4 + 9)(4 - 1) = 13 \times 3 = 39$ birds. The total for the first four years is $a_1 + a_2 + a_3 + a_4 = (10)(0) + (11)(1) + (12)(2) + (13)(3) = 0 + 11 + 24 + 39 = 74$ birds.

Solve the Problem an=(n+9)(n−1)a _ { n } = ( n + 9 ) ( n - 1 )an​=(n+9)(n−1)

Solve the Problem $a _ { n } = ( n + 9 ) ( n - 1 )$