Question 147347
Rewrite as

4m^2-20m+25=0

where
am^2+bm+c=0  is the form we're interested in.

so
b^2-4ac=(-20)^2-4*4*25=400-400=0


Since the discriminant is 0 we shall have 1 solution. You can see why this is so from the quadratic formula:
{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}
If we eliminate the root due to a zero, the +/- is irrelevant and leaves only -b/2a  as the solution of x.