The first and last terms of an AP are 1 and 11 respectively

Question:

The first and last terms of an AP are 1 and 11 respectively. If the sum of its terms is 36, find the number of terms.

Solution:

Given: the sum of its terms is 36, the first and last terms of an AP are 1 and 11.

To find: the number of terms

Sum of AP using first and last terms is given by

$\mathrm{S}_{\mathrm{n}}=\frac{\mathrm{n}}{2}(\mathrm{a}+\mathrm{l})$

$36 \times 2=\mathrm{n}(1+11)$

$\mathrm{n}=6$

 

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