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Grazes
If a+b=140 and ar+br=35. What is the value of r?
First this you need to do is solve for r ar+br=35 r(a+b)=35 r=35/(a+b)
The next thing is use substitution so you only have one variable a+b=140 a=140-b
I didn't think of turning r into terms of ab. Thanks!
Then substitute 140-b in the equation you solved for r r=35/((140-b)+b) r=35/140