Answer:
106
Step-by-step explanation:
just subtract 243-137
The equations are

,
The graphs of the solutions (x, y) of these equations are 2 parabolas, since the right hand side expressions are polynomials of degree 2.
The solution/s of the system are the x-coordinates of the point/s of intersection of the parabolas.
The solutions of the first equation form a parabola looking downwards (since the coefficient of x^2 is -), and the second, a parabola opening upwards (since the coefficient of x^2 is +).
We can draw both parabolas, but to find the solution we still need to solve the system algebraically.
The algebraic solution of the system is:

, so
the solutions are x=-1 and x=1.
The graph of the system is drawn using desmos.com
If we are allowed to use a graphic calculator, we can draw both graphs and point at the solution.
Answer:
462 ways
Step-by-step explanation:
One book never selected means 12 - 1 = 11.
So to find the number of ways, 11C5 which equals to: 11!/(5!(11-5)!) = 462
Answer:

Step-by-step explanation:
The mean is the sum of the allowances divided by the number of students.
