Question

The geometric mean of 1 and a is 9. Find a.

The arithmetic mean of 1 and a is 9. Find a.

Answer 1

The arithmetic mean of 1 and a is 9.

so (1+a)/2 = 9

a = 9*2 - 1

= 17

The geometric mean of 1 and a is 9.

so sqrt(1*a) = 9

1*a = 9^2

a = 81

Answer 2

The arithmetic mean is the sum divided by the number of numbers.
9 = (1 +a)/2
2*9 = 1 +a
2*9 -1 = a = 17

The value of "a" is 17.