Whats the ratio between $76,500 to $100,000

The number of revolutions of two pulleys is inversely proportional to their diameters. if a 24-inch diameter pulley making 400 revolutions per minute is belted to an 8-inch diameter pulley, find the number of revolutions per minute of the smaller pulley.

What number should be added to both sides of the equation to complete this square? x^2-10x=7

If 25% of y is 30, what is 60% of y?