Classic Math Question on EVERY SAT- How do it???

Discus: SAT/ACT Tests and Test Preparation: October 2003 Archive: Classic Math Question on EVERY SAT- How do it???
 By Howdydoody (Howdydoody) on Thursday, October 09, 2003 - 06:25 pm: Edit

What is the average of all of the intengers from
-39 to 40, inclusive?

What is the quick way to do this problem? Thank you.

 By Zephyrmaster (Zephyrmaster) on Thursday, October 09, 2003 - 06:27 pm: Edit

I think you can add the top and last...

(-39+40)/2 and find an average...

this is coming from Mr. 650 Math Twice, so don't take my word for it... at ALL.

 By Howdydoody (Howdydoody) on Thursday, October 09, 2003 - 06:33 pm: Edit

Hmmm...the answer is .5..looks like you may be on to something...does this always work?

 By Akaflex (Akaflex) on Thursday, October 09, 2003 - 06:54 pm: Edit

u got to be like okay u know from -39 to + 39 they cancel out so 40 will be the some and there will be 80 integers including 0 so u divide 40/80

 By Pcqo (Pcqo) on Friday, October 10, 2003 - 12:57 pm: Edit

40*41/2 - (39*40/2)
_____________________ = 0.5
80

 By Drusba (Drusba) on Friday, October 10, 2003 - 01:08 pm: Edit

If I am remembering my trick math correctly, the original formula given by Zephyrmaster above -- add the first and last integers and then divide by 2 -- should always work.

 By Xiggi (Xiggi) on Friday, October 10, 2003 - 01:28 pm: Edit

It does

 By Testtaker (Testtaker) on Friday, October 10, 2003 - 02:33 pm: Edit

You could just find the sum which is 40 and divide by the number of integers, which is 80.