Question

Write the sum using summation notation, assuming the suggested pattern continues.

-9 - 4 + 1 + 6 + ... + 66
Never learned what to do when missing a number...

Answer 1

As you seem, 5 is added everytime

Answer 2

-9 + 5 = -4
-4 + 5 = 1
1 + 5 = 6

So the next number will be 6+5 = 11