The first term of the arithmetic progression is 2.7, and the difference is -0.3.

The first term of the arithmetic progression is 2.7, and the difference is -0.3. What is the number of the member of this progression equal to -2.7?

Let’s insert into the formula of the n – th term of the arithmetic progression the value of the difference between the progression and its first term and the n – th term equal to -2.7 and from this formula we express the ordinal number of this term.

an = a1 + b * (n-1).

-2.7 = 2.7 + (-0.3) * (n – 1).

-2.7 – 2.7 = -0.3 * n + 0.3.

-0.3 * n = -5.7.

n = -5.7 / (-0.3) = 19.

Answer: -2.7 is the nineteenth term of the arithmetic progression.