Question

A model boat is made to a scale of 1:20 inches. If the 1:20 model boat is 15 inches wide, how wide is the actual boat

Answer 1

If the scale is 1:20, then the scale model would be 1/20th the size of the real thing. This means that to find the actual value, you would need to multiply the scaled-down value by 20. 
15 * 20 = 300
It is 300 inches wide, or 25 feet.
Hope that helped! =)