umsami Posted August 27, 2013 Share Posted August 27, 2013 Here is a list of numbers. Circle the multiples of 5. Two of the multiples of 5 are common multiples of 5 and X. 4 5 7 10 15 24 25 27 35 42 45 49 What is X? The answer is (according to the teacher's manual) 3 or 15. What is their thought process? I can work back and see it, but I'm not sure how to help my son do it. We can list all the multiples of 5. (5, 10, 15, 20, 25, 30, 35, 40, 45) But then how do we figure out which are for X? Quote Link to comment Share on other sites More sharing options...
EKS Posted August 27, 2013 Share Posted August 27, 2013 The only thing I can think of is that you know you're looking for a pair of numbers that have a second common factor (x). The even multiples (10, 20, etc) all have the common factor 2, but there are four of them, not two. It's a very strange problem. Quote Link to comment Share on other sites More sharing options...
mom2bee Posted August 27, 2013 Share Posted August 27, 2013 1) List the multiples of 5: 5, 10, 15, 25, 35, 45. 2) Factor those multiples to see which have a common factor other than 5. 05 = 5 * 1 10 = 5 * 2 15 = 5 * 3 25 = 5 * 5 35 = 5 * 7 45 = 5 * 9 OR 5 * 3 * 3 Therefore both 15 and 45 are multiples of both 5 and 3, with 3 being x. Quote Link to comment Share on other sites More sharing options...
umsami Posted August 27, 2013 Author Share Posted August 27, 2013 Thanks mom2bee. :) Quote Link to comment Share on other sites More sharing options...
blondeviolin Posted August 27, 2013 Share Posted August 27, 2013 Your multiples of 5 are 15, 25, and 45. Of those multiples, 15 and 45 are also multiples of 3 or 15. Quote Link to comment Share on other sites More sharing options...
umsami Posted August 27, 2013 Author Share Posted August 27, 2013 "It's a very strange problem." Thank you for making me feel better. :) Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.