Solve for r
r=10
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4\times 5=r\times 2
Variable r cannot be equal to 0 since division by zero is not defined. Multiply both sides of the equation by 4r, the least common multiple of r,4.
20=r\times 2
Multiply 4 and 5 to get 20.
r\times 2=20
Swap sides so that all variable terms are on the left hand side.
r=\frac{20}{2}
Divide both sides by 2.
r=10
Divide 20 by 2 to get 10.
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