How to solve order of operations w/missing number  TOPIC_SOLVED

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How to solve order of operations w/missing number

Postby sahmof2boys on Wed Aug 15, 2012 2:17 am

Problem

76-?/2=41 Please explain the rule for solving these types of problems when there's a missing number. Thanks Is there a site that I can go to that will explain the step by step process on resolving these types of problems. I need help explaining these to my son who will be starting middle school in a few weeks. thanks in advance
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Postby stapel_eliz on Wed Aug 15, 2012 12:04 pm

sahmof2boys wrote:Problem: 76-?/2=41

Please explain the rule for solving these types of problems when there's a missing number.

To my knowledge, there is no "rule" or "formula". You just have to allow yourself enough time to plod through various possibilities until you happen upon a solution.

Grab some scratch paper, and have fun! :wink:
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Re: How to solve order of operations w/missing number  TOPIC_SOLVED

Postby LoveMath on Tue Sep 04, 2012 1:15 am

:nono: You don't want to "plod through various possibilities until you happen upon a solution". That would take some time. You want to solve the problem by substituting the ? with an x. This gives:

(76-x)/2 = 41. Then the first thing to do is to get rid of the denominator. This can be done by multiplying both sides by 2. You then get
76-x = 41(2)
76-x = 82 Then by subtracting 76 from both sides gives
-x = 6 And now you multiply both sides by -1 in order to make x positive. That is,
-1(-x) = -1(6)
x = -6

This checks out since:
(76-(-6))/2 = (76+6)/2 = 82/2 = 41

:clap:
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Re: How to solve order of operations w/missing number

Postby MrAlgebra on Sat Sep 15, 2012 4:12 pm

With 76-?/2=41, you would write the equation out as 76 - x/2 = 41 and solve for x. Note that there are no parentheses around the 76 - x part, so the first thing you would be doing in the problem is dividing x by 2.

I would start out by subtracting 76 from both sides:

76 - x/2 = 41
76 - x/2 - 76 = 41 - 76
76 - 76 - x/2 = 41 - 76
- x/2 = -35

Now I would multiply both sides by -1 to get rid of the negatives.

-x/2 * -1 = -35 * -1
x/2 = 35

Now I would multiply both sides by 2 to get rid of the division by 2 on the left side of the equation.

x/2 * 2 = 35 * 2
x = 70

Now you should check your answer by putting 70 into the original equation to see if you get something that makes sense.

76 - ?/2 = 41
76 - 70/2 = 41
76 - 35 = 41
41 = 41
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Re: How to solve order of operations w/missing number

Postby hanifkhan on Mon Dec 22, 2014 8:20 am

Thanks Is there a site that I can go to that will explain the step by step process on resolving these types of problems.
I need help explaining these to my son who will be starting middle school in a few weeks.



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