Question

Find the sum of the finite arithmetic sequence.
Sum of the first 80 positive odd integers

Answer 1

6400

Explanation:

We have 1 + 3 + 5 + ... + 155 + 157 + 159.

We can use Gauss's strategy.

Since we are adding 80 numbers, there are 40 pairs. Each pair adds up to 1 + 159 = 160. (Notice that 3 + 157, 5 + 155 = 160)

Thus, because there are 40 pairs and each pair adds up to 160, we have 160 * 40 = 6400.

I hope this helps!