
Elementary Math Fractions, Percentages, Word Problems, Equations, Inequations, Factorization, Expansion 
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April 11th, 2018, 01:26 AM  #1 
Senior Member Joined: Aug 2014 From: India Posts: 420 Thanks: 1  [average] What is the total weight of the boys?
In a class, the average weight of girls is six kg less than the average weight of boys. The numbers of boys and the numbers of girls are the same. The average weight of boys is three kg more than the numerical value of the number of girls. If the average weight of the girls is 22 kg, What is the total weight of the boys? [Ans: 700 Kg] My try: If average weight of girls is 22 and then boys is 22 + 6 = 28 because of the average weight of girls is six kg less than the average weight of boys. In second sentence it tells us, The average weight of boys is three kg more than the numerical value of the number of girls. So I assume numerical value of the number of girls is 100. Then The average weight of boys is 100 + 3 = 103. After this I can't able to continue. Last edited by Ganesh Ujwal; April 11th, 2018 at 01:37 AM. 
April 11th, 2018, 01:50 AM  #2 
Senior Member Joined: Oct 2009 Posts: 841 Thanks: 323  
April 11th, 2018, 01:51 AM  #3  
Senior Member Joined: Jun 2015 From: England Posts: 915 Thanks: 271  Quote:
I am going to have one last try to help you, because you have laid out your attempt in the correct fashion. So you correctly deduced that No of boys = 22 = 6 = 28. Then you went astray because you assumed something. Now we come to the nitty gritty of why it is difficult to help you. You fail to engage in useful conversation with someone at this point because you have already decided in your own mind how things should proceed and it upsets you when things don't work that way. In particular when someone asks a question intended to help overcome the stumbling block, you don't answer. So here is my question. Why did you assume rather than just saying let the number of girls be G (currently unknown)? Note I find that as the maths gets more complicated and difficult one needs more question and answer exchanges to work through it. It is always good to break it down to small steps at first and take them one at a time.  
April 11th, 2018, 01:59 AM  #4 
Senior Member Joined: Aug 2014 From: India Posts: 420 Thanks: 1  
April 11th, 2018, 02:00 AM  #5 
Senior Member Joined: Oct 2009 Posts: 841 Thanks: 323  
April 11th, 2018, 02:11 AM  #6 
Senior Member Joined: Aug 2014 From: India Posts: 420 Thanks: 1  
April 11th, 2018, 02:19 AM  #7 
Senior Member Joined: Jun 2015 From: England Posts: 915 Thanks: 271  Perhaps someone in India was misleading you. I have discussed mathematics with many Indians and never come across that before. But thank you for replying. Here is a much better method. Start by making a list or table of the information in the question. Place numbers against what you know and letters against what you don't know. You may not have to find out what all the letters are but that list is invaluable. So I would start by listing Av Weight of boys P Av Weight of girls Q = 22 Number of boys B Number of girls G Now you know there are 3 unknowns left so you require 3 equatiosn to find them all. You have written down the first one P = Q + 6 = 22 + 6 = 28 So you need 2 more equations. Can you look at the question again and see if you can write down any more equations? Then as you work out more values the table comes into its own as you can record the newly calculated values there as you go along. 
April 11th, 2018, 02:21 AM  #8 
Senior Member Joined: Aug 2014 From: India Posts: 420 Thanks: 1 
Remaining part: I figured it myself: 22 = x  6, x = 28, average weight of boys = 28 kg 28 = g + 3, g = 25, number of girls = 25 g = b, 25 = b, number of boys = 25 Total weight of boys = average weight of boys x number of boys Total weight of boys = 28kg x 25 = 700kg 
April 11th, 2018, 02:22 AM  #9 
Global Moderator Joined: Dec 2006 Posts: 20,835 Thanks: 2162  You found that the boys have average weight 28 kg, so there are 25 girls. There are as many boys as girls, so there are 25 boys, which implies that their combined weight is 25 × 28 kg = 700 kg.

April 11th, 2018, 02:30 AM  #10 
Senior Member Joined: Jun 2015 From: England Posts: 915 Thanks: 271 
There you can do it. Do you not think the formal method I showed you would help organise your thoughts? 

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