Answer:
9 friends
Explanation:
The group is made up of F number of friends, so the current cost per friend is 360000/F.
If one more friend is included in the purchase, the cost per friend will be: 360,000/(F + 1)
360,000/(F + 1) = 360,000/F - 4,000
360,000/F - 360,000/(F + 1) = 4,000
360,000 (1/F - 1/(F + 1) = 4,000
90(1/F - 1/(F + 1) = 1
90 [(F + 1) - F] / [F(F + 1)] = 1
90 (F + 1 - F) / [F(F + 1)] = 1
90 { 1 / [F(F + 1)]} = 1
90 / [F(F + 1)] = 1
90 = F(F + 1)
90 = F² + F
F² + F - 90 = 0
(F + 10) (F - 9) = 0
F = -10 or 9
Since people cannot be negative, then the total number of friends is 9.