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What is the inverse variation equation if f(x)=18 when x = 12?

What is the missing constant term in the perfect square that starts with x^2 -20x

An advertising firm has an old computer that can prepare a whole mailing in 6 hours. with the of newer model the job is complete in 2 hours. how long would it take the newer model to do the job alone?

On saturday a souvenir shop had 125 customers.sixty four percent of the costumers paid with a credit card. how many costumers paid with cash?