How much would a 20% tip be on a $48 restaurant bill?

Planning for the possibility that your home might get struck by lighting and catch on fire is part of a plan for ?

Agreeting card company can produce a box of cards for $7.50. if the initial investment by the company was $50,000, how many boxes of cards must be produced before the average cost per box falls to $10.50?

What is the missing step in this proof ?