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What is the sum of (86+87+88+\cdots+140)?

Answer and explanation

Correct answer: 6215

This is an arithmetic sequence from 86 to 140. The number of terms is \(140-86+1=55\), with first term 86 and last term 140. Therefore, the sum is \(\frac{55}{2}(86+140)=\frac{55}{2}\times226=6215\). A value such as 6185 can result from an error in counting the terms or finding the average. Exam tip: for consecutive integers, always use \(n=\text{last}-\text{first}+1\).

Related tags

MathematicsArithmetic ProgressionConsecutive IntegersSeries SumNatural NumbersSum Of First N Natural NumbersSequences And ProgressionsClass 9 Mcq

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