Question

Find the sum (–5) + (–8) + (–11) + .................... + (–62).

Answer 1

Here, $$a = -5, \ d = -3, \ l = -62$$. 

$$-5 + (n - 1)(-3) = -62$$

$$\Rightarrow n = 20$$ 

$$S_{20} = \frac{20}{2}(-5 - 62)$$

$$= 10(-67)$$

$$= -670$$