You are given a geometric progression (bn), the denominator of which is 1/5, b1 = 500.

You are given a geometric progression (bn), the denominator of which is 1/5, b1 = 500. Find the sum of the first 5 of its members.

The sum of the members of the geometric progression is found by the formula Sn = b1-bn * q / 1-q. The 5th term of the progression is found by the formula bn = b1 * q in step n-1 = 500 * (1/5) in step 4 = 500 * 1/625 = 4/5. Sn = (500-4 / 5 * 1/5) / (1-1 / 5) = (500-4 / 25) / (4/5) = ((12500-4) / 25) * 5/4 = (12496/25) * (5/4) = 3124/4 = 624.8