If 1/a + 1/b =1/c and ab=c, what is the average of a and b?

If we solve the left side of the given equation,
                                  1/a + 1/b = 1/c
 we get an answer of,
                                    b+a / ab = 1/c
Since ab = c, we can conclude that b + a is 1. The average of these two numbers is equal to there sum divided by 2. The answer is therefore equal to 0.5. 

First step is to get rid of the square root. remember that a square root is the same as raising to the (1/2) power. see below: multiply exponents per exponent rules to get: remember you subtract exponents from the denominator and add exponents in the numerator so: simplify further: so a is the correct choice. if you don't understand this google exponent rules and it will you understand. look at the image results.