If three positive numbers a, b and c are in A.P. such that abc=8, then the minimum possible value of b is:

In an arithmetic progression (A.P.), the middle term (b in this case) is the average of the other two terms. So, we can write b = (a + c) / 2.

Given that abc = 8, we can substitute b into this equation to get: a * (a + c) / 2 * c = 8.

Solving this equation for c, we get c = 16 / a^2.

Substituting c back into the equation for b, we get b = (a + 16 / a^2) / 2.

To find the minimum value of b, we can take the derivative of this function with respect to a and set it equal to zero. This gives us a = sqrt(8), or approximately 2.83.

Substituting a = 2.83 back into the equation for b, we get b = (2.83 + 16 / 2.83^2) / 2 = 2.

So, the minimum possible value of b is 2.