SOLUTION: What is the sum of all of the odd numbers from 21 to 39?

Question 1023337: What is the sum of all of the odd numbers from 21 to 39?
Found 6 solutions by addingup, Emilym1234, ikleyn, MathTherapy, Shin123, Alan3354:
Answer by addingup(3677)   (Show Source): You can put this solution on YOUR website!
1)write them out: 21+23+25 etc
2)use your calculator.
Answer by Emilym1234(10)   (Show Source): You can put this solution on YOUR website!
First, make a list of all the odd numbers between 21 and 39.
21,23,25,27,29,31,33,35,37,39
Then add them with a calculator.
If you don't have one,
They add up to 300! Hope this helped :)
Answer by ikleyn(52776)   (Show Source): You can put this solution on YOUR website!
.
What is the sum of all of the odd numbers from 21 to 39?
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Use the formula 1 + 3 + 5 + 7 + . . . + (2n-1) = . In your case 1 + 3 + 5 + 7 + . . . + 39 = , 1 + 3 + 5 + 7 + . . . + 19 = , so the difference = = 400 - 100 = 300. It is exactly the sum 21 + 23 + . . . + 39, and it is your answer.

Answer by MathTherapy(10551)   (Show Source): You can put this solution on YOUR website!

What is the sum of all of the odd numbers from 21 to 39?

This is an AP. Use the formula for the finite sum of the terms of an AP.
Answer by Shin123(626)   (Show Source): You can put this solution on YOUR website!
If you add all the ones first it is, If you add the tens, 250+50=300
Answer by Alan3354(69443)   (Show Source): You can put this solution on YOUR website!
What is the sum of all of the odd numbers from 21 to 39?
--------
10 odd numbers.
--> 5 pairs:
21 + 39
23 + 37
.
.
.
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Each pair is 60
5*60 = 300

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