Question 5036
From the problem description, you can write:
 n/2 + 1/n = 51/n where n is the unknown number.  Multiply through by n to clear the fractions.
(n^2)/2 + 1 = 51  Now multiply through by 2.
n^2 + 2 = 102  Subtract 2 from both sides.
n^2 = 100  Take the square root of both sides.
n = +/- 10

Both 10 and -10 will work here.