Question

1,2,1,2,1,2... what is the sum of the first 20 terms?

Answer 1

See a solution process below:

Explanation:

If every other term in the sequence is a `1`, then the first 20 terms has 10 `1`'s or `10 xx 1 = 10`

Likewise, if every other term in the sequence is a `2`, then the first 20 terms has 10 `2`'s or `10 xx 2 = 20`

When can add these together giving: `10 + 20 = 30`