At the AoPS office, mice vary inversely with cats, that is, $\text{mice}=\frac{k}{\text{cats}}$, for some value of $k$. When there are $3r-19$ cats, there are $2r+1$ mice, and when there are $6r-27$ mice, there are $r-5$ cats. Find $k$.
+87 https://web2.0calc.com/questions/confusing-algebra: Link To Actuall Response
Some people seem to have some difficulty in understanding how r=7 and k=30 were obtained above!!!.
Solve for k in equation (1) above and you should get this:
k = 6 r^2 - 35 r - 19
Solve for k in equation (2) above and you should get this:
k = 6 r^2 - 57 r + 135
Equate the above 2 equations and solve for r:
6 r^2 - 57 r + 135 = 6 r^2 - 35 r - 19, solve for r
-57r +35r =-19 - 135
-22r = - 154
r = 7 sub this into one of the equations above and you should get:
k = 30
