Question

Jerry writes down all the odd numbers $1, 3, 5, 7, \dots,$ up to $999$. what is the sum of all the numbers he writes down?

Answer 1

250000

Step-by-step explanation:

To find the sum of all the numbers, we have to know how many numbers there are in this series. The formula to find that is n = (aN - a1)/d +1, (d is the distance between 1 number to the next) which is (999 - 1)/2 + 1 =500. Now, to find the sum, you use the formula (a1 + an) x n/2 and you substitute the numbers in to find (999 + 1) x 500/2 which is 250000