What is the sum of all the odd numbers up to 200000?

Answer 1

Assuming you mean starting from 1, ie the sum 1 + 3 + 5 + ... + 199,999; then

sum = 1/2 x (first_number + last_number) x (number_of_numbers)

= 1/2 x (1 + 199,999) x ((199,999 - 1)/2 + 1)

= 10,000,000,000

Answer:

As a slightly different approach to the same anser:

Thee are 100,000 odd numbers between 1 and 200,000

Adding the pairs (1+199,999, 3+199,997 etc which each equal 200.000) gives you 50,000 sums of 200,000

or (50x200)x 1,000,000 = 10,000,000,000