arithmetic progression

Question

The sum of the first 20 terms of an AP with first term 5 and common difference 3 is

RankGuru · Accepted Answer

1. **Identify Data**: $a = 5$, $d = 3$, $n = 20$.
2. **Sum Formula**: $S_n = \frac{n}{2} [2a + (n - 1)d]$.
3. **Substitution**:
   - $S_{20} = \frac{20}{2} [2(5) + (20 - 1)(3)]$
   - $S_{20} = 10 [10 + (19)(3)]$
4. **Final Computation**:
   - $S_{20} = 10 [10 + 57] = 10 	imes 67 = 670$.

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