Answer:
10 friends.
Step-by-step explanation:
Givens
Sum = 275
a1 = 5
d = 5
n = ?
Formula
Sum = ( (2*a1) + (n - 1)*d) * n / 2 Substitute the knows.
Solution
Sum = ( 2 * 5 + (n - 1)*5 ) * n/2 Combine on the right
275 = (10 + (n - 1)5 ) n/2 Multiply by 2 and remove the brackets.
550 = (10 + 5n - 5) * n Combine
550 = (5 + 5n ) * n Remove the brackets
550 = 5n + 5n^2 Subtract 550 from both sides.
5n^2 + 5n - 550 = 0 Divide by 5 (all terms are divisible by 5)
n^2 + n - 110 = 0 Factor
(n + 11)(n - 10) = 0
The only root that has any meaning is n - 10 = 0
n + 11 means Jane has - 11 friends. That has no meaning at all.
n - 10 = 0
n = 10
She had 10 friends who got stickers.
