Find the sum of all whole numbers 1 to 100 without a calculator and not adding the number one by one.

Question

1+2+3+4+....+97+98+99+100.

Use at least one sentence stem to explain your thinking. 

Answer 1

The sequence of numbers (1, 2, 3, … , 100) is arithmetic and when we are looking for the sum of a sequence, we call it a series. There is special formula we can use to find the sum of a series:

Use the formula:  

Plug in 100 for n because n is the number of terms in the series: