Solve for y
y=5
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y\times 42=10\times 21
Variable y cannot be equal to 0 since division by zero is not defined. Multiply both sides of the equation by 10y, the least common multiple of 10,y.
y\times 42=210
Multiply 10 and 21 to get 210.
y=\frac{210}{42}
Divide both sides by 42.
y=5
Divide 210 by 42 to get 5.
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