Browse our archive of questions and answers below or to access our old forum database of over 10000 questions and answers please visit the old Ask@ forum.

 Number Tricks Last Post 30 May 2012 12:22 PM by Andrej. 1 Replies. Sort: Oldest First Most Recent First
 Prev Next You are not authorized to post a reply.
 Author Messages
alastair

Basic Member
Posts:132

 30 May 2012 05:40 AM Ms. Arroyo asked the class to see if they could find the sum of the first 50 odd numbers. As everyone settled down to their addition, Terry ran to her and said, "The sum is 2,500." Ms. Arroyo thought, "Lucky guess," and gave him the task of finding the sum of the first 75 odd numbers. Within 20 seconds, Terry was back with the correct answer of 5,625. How does Terry find the sum so quickly?
Andrej

New Member
Posts:1

 30 May 2012 12:22 PM Because he tried to make an arithmentic progression with them: 101- the 50th odd number 1- 1st odd number Sn= (101-1)/2*50=50*50=50^2 151- 75 odd number Sn= (151-1)/2*75=75*75=75^2, and so on....
 You are not authorized to post a reply. Engineering Questions and Answers --Chemical/Material Engineering --Civil/Structural Engineering --Electrical Engineering --Mechanical Engineering --Student Questions --General Engineering --Puzzles Community Support --Jobs