In mathematics, 'is' would be the equal sign. And 'of' would be the multiplcation sign. The missing number would be any variable.
56 is 28% of a number would be translated algebraically to:
Solving for x, we get:
Divide 28 on both sides
Multiply 100 on both sides
56 is 28% of 200
56 is 28% of a number would be translated algebraically to:
Solving for x, we get:
Divide 28 on both sides
Multiply 100 on both sides
56 is 28% of 200