Lesson: Calculating Combinations

Comment on Calculating Combinations

God bless u.you soo good

Thank you.

you are great!!! THIS SHORT CUT IS IS NOT THOUGHT IN SCHOOLS.

thank you, YOU ARE BEST MATH TEACHER.

-> I HAVE ONE MORE QUESTION -> IF I HAVE DONE A WRONG STEP CALCULATION NPR INSTEAD OF NCR FOR "ORDER DOESNT MATTER" SELECTION QUESTIONS, CAN i STILL GET THE CORRECT ANSWER BY DIVIDING THE OUTCOME WITH 2.

-> IN SHORT WHAT IS MEANT IS => COMBINATION=1/2(OUTCOME OF PERMUTATION) AT LEAST WHEN THERE IS A TOTAL VALUE N A EVEN NUMBER. HOW ABOUT THE APPROACH? ALWAYS DIVIDE OUTCOME BY 2 AND RECHECK WITH ANSWER CHOICES? WILL THIS WORK?
PLEASE RPLY -THANKS AND REGARDS VINEET
greenlight-admin's picture

Thanks for the kind words, Vineet.

In general, if you accidentally use nPr (instead of nCr), you can find the correct result if you divide your calculation by r!

So, for example, if you accidentally calculate 5P2 (instead of 5C2), you can find the correct result if you divide your calculation by 2!

Does that help?

Cheers,
Brent

ASIDE: I'm not a big fan of permutations as they pertain to GRE counting questions. For more on this, read: https://www.greenlighttestprep.com/articles/combinations-and-non-combina...

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