Question
If the first term of the arithmetic progression is 18,
the common difference is 5, and the number of terms in the series are 40, then find the sum of the series.Solution
First term (a) = 18 Common difference (d) = 5 Number of terms (n) = 40 Required sum = (n/2) {2a + (n – 1) × d} = (40/2) × {2 × 18 + (40 – 1) × 5} = 20 × (36 + 39 × 5) = 20× (36 + 195) = 20 × 231 = 4620
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