Given a geometric progression (Bn), the denominator of which is 5, B 1 = 4/5 find the sum of the first 4 of its members.

Knowing which number is in the first place in a given sequence, as well as the denominator of this progression, we find the members of this progression in the second, third and fourth places, and then we find the sum of these numbers.

We find the member of the sequence that is in second place:

b2 = b1 * q = (4/5) * 5 = 4.

Find the third-place member of the sequence:

b3 = b2 * q = 4 * 5 = 20.

Find the fourth member of the sequence:

b4 = b3 * q = 20 * 5 = 100.

Let’s calculate the sum of the first 4 members of this progression:

b1 + b2 + b3 + b4 = 4/5 + 4 + 20 + 100 = 124 4/5.

Answer: the sum of the first 4 members of this progression is 124 4/5.