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how do you figure out -2/n =10/6

I am trying to help my son with his 7th grade math homework. 
The problem is:
-2/n us equal to 10/6 I want to learn how to figure this out so I can show my son. 

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Parviz F. | Mathematics professor at Community CollegesMathematics professor at Community Colle...
4.8 4.8 (4 lesson ratings) (4)
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-2/n = 10/6
 
-2/n = 5/3
 
 This is simple problem of proportion 3 rd grade
 
   Cross multiply:
   -2( 3) = 5n
 
    n = -6/5
Kyle M. | Certified Educator with Masters, Tutoring 3rd Grade Through CollegeCertified Educator with Masters, Tutorin...
4.9 4.9 (150 lesson ratings) (150)
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Obviously, in these kind of examples, the solution must demonstrate that both sides are equal. The strategy is to discover which number n will make the fraction equivalent.
Start with the numerators, those numbers at the top of the fractions, -2 & 10. Is there a factor of 10 that will leave us with -2?
10/-2=-5; 10/-5=-2
So -5 is the factor 10 that leaves us with -2. Now we divide 6 by that same factor:
6/-5=-1.2
Another way to do this is cross-multiplication. Multiply n by 10 & multiply -2 by 6. These two products must be equal:
-12=10n
Use basic algebra to solve for n:
-12/10=n
-1.2=n
John L. | Experienced and Patient TutorExperienced and Patient Tutor
4.9 4.9 (123 lesson ratings) (123)
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Michael,
             you set up a proportion , two equal fractions or ratios. In this case- 2/N = 10/6
 
then you cross multiply -2 x 6 = 10 x N
 
which gives you- 12 = 10N
 
 
to find out what N equals divide each side of the equation by 10  so- 12/10 + 10N/10
 which  gives you -1.2 = N
 
 
so  -2/1.2 = 10/6