3.
consecutive odd numbers starting at
1 are added together. their sum is
400. how many numbers were
added?

20

Step-by-step explanation:

Sn = (n/2)(a1 + a1 + d(n-1)), where S = sum, a1 = first term, n = number of terms, d = common difference

400 = (n/2)(1 + 1 + 2(n - 1))

400 = (n/2)(2  + 2n - 2)

400 = (n/2)(2n

400 = n2

20 = n

Twenty numbers are in the set.

16

step-by-step explanation:

2 x 40 = 80

80/5

= 16