Answer:
6 friends (4 pay € 1.75 and 2 pay € 1)
Step-by-step explanation:
We have to:
x = friends
y = payment
x * y = 9
y = 9 / x
It follows from the problem:
(x-2) * (y + 0.25) = 9 - 2
(x-2) * (9 / x + 0.25) = 7
x * 9 / x + 0.25 * x - 2 * 9 / x - 2 * 0.25 = 7
9 + 0.25 * x - 18 / x - 0.5 = 7
multiply by 100
100 * 0.25 * x - 100 * 18 / x + 100 * (9 - 0.5 - 7) = 0
25 * x - 1800 / x + 150 = 0
multiply by x
25 * x ^ 2 + 150 * x - 1800 = 0
we factor:
(x - 6) * (x + 12) = 0
x = 6
x = -12
The positive value is taken: x = 6
Each one had to pay = 9/6 = € 1.5
But as two pay € 1, 4 will pay € 0.25 more: 1.5 +0.25 = € 1.75
Thus :
(4 * 1.75) +2 (1) = € 9
Therefore, they are 6 friends (4 pay € 1.75 and 2 pay € 1)
