It will either be given directly in the problem, or two consecutive terms will be given from either the start or the end of the arithmetic progression. Let the common difference be denoted by d.;
, First term and last term are required to find out the number of terms of an Arithmetic Progression. Identify them and note them down. Let the first term be represented by A and let the last term be represented by L.
 Divide the common difference (d) into the difference between the last term (L) and the first term (A), and then add 1.
Find out the common difference.
Identify the first and last term of the sequence.
Calculate the number of terms by using the following formula: Let the number of terms be represented by n. The formula is:

n = (L-A)/d + 1

The formula is very simple.
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