Bunuel wrote:

Which of the following sets contain numbers that are factors of M, if M is the sum of all integers from 21 to 85, inclusive?

A. (5, 7)

B. (2, 65)

C. (1, 13)

D. (3, 17)

E. (2, 9)

M is the sum of all integers from 21 to 85 = 21+22+23+......+85

Count of integers from 21 to 85 = 85 - 20 = 65

Sum of numbers in Arithmetic progression = [(first term + Last Term)/2] * Number of termsi.e. M = (21+85)*65/2 = 3445

Now, 3445 = 5*689 = 5*13*53

Answer: Option B

Bunuel : The question should be "Which of the following sets contains PRIME numbers that are factors of M"

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired. If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links:

Quantitative |

Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.

_________________

Prosper!!!

GMATinsight

Bhoopendra Singh and Dr.Sushma Jha

e-mail: info@GMATinsight.com I Call us : +91-9999687183 / 9891333772

Online One-on-One Skype based classes and Classroom Coaching in South and West Delhi

http://www.GMATinsight.com/testimonials.html

22 ONLINE FREE (FULL LENGTH) GMAT CAT (PRACTICE TESTS) LINK COLLECTION