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June 22nd, 2018, 05:41 PM  #1 
Newbie Joined: Feb 2018 From: California Posts: 17 Thanks: 1  Averages
I have a few questions on averages. I am curious to see different strategies on how to answer these. How would you answer these using elementary school math ONLY? 1. Jill and Jim are twins. At the age of 2, their average weight is 12 kilograms. In the next year, Jill gains 2 kilograms and Jim gains 4 kilograms. What is their average weight when they are 3 years old? 2. The average weight of Mark and Mina is 25 kilograms. A year later, their average weight is 30 kilograms. During this year, Mina gained 2 kilograms. How many kilograms did Mark gain? 3. John takes two exams, and his average score is 84. He then gets a score of 100 on the third exam. What is his new average score? 4. After taking two exams, Jane’s average score is 88. What score must Jane make on the third exam so that her new average score is 90? 5. Sam receives the following scores on his English tests: 63, 84, 96 . What average score does he need on the last two tests in order to maintain an 85 
June 22nd, 2018, 06:14 PM  #2  
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 12,771 Thanks: 862  Quote:
(a + b + 6) / 2 = ? OR: they gained an average of (2 + 4)/2, so new average = ?  
June 22nd, 2018, 06:27 PM  #3 
Newbie Joined: Feb 2018 From: California Posts: 17 Thanks: 1 
Thank you. I guess I am most interested in how to go about numbers 4 and 5 without using algebra. How would you teach this without using algebra? The only way I can think is to do number 5 is: (243 + x) / 5 = 85, then solve for x.

June 22nd, 2018, 06:40 PM  #4 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 12,771 Thanks: 862  
June 22nd, 2018, 08:10 PM  #5 
Newbie Joined: Feb 2018 From: California Posts: 17 Thanks: 1 
Right, I was thinking of x as the sum of the 2 scores, then I was going to divide x by 2 to get the average score. But, yes, thank you for that. I am supposed to teach how to do this to students who don't yet know algebra.

June 23rd, 2018, 02:35 AM  #6  
Math Team Joined: Jan 2015 From: Alabama Posts: 3,248 Thanks: 887 
[QUOTE=mjsilverfly;595808]I have a few questions on averages. I am curious to see different strategies on how to answer these. How would you answer these using elementary school math ONLY?[/math] The "average" of n numbers is their total divided by n. Conversely, the total is the average multiplied by n. Quote:
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