The width of the actual yard is 50 feet wide. Since the scale from the drawing to real life is 1 inch for every 10 feet, simply multiply 1:10 by the same number on both sides to get an equivalent ratio using the given scale. Basically, 1 inch : 10 feet * 5:5 equals 5 inches for every 50 feet.
Alternative:
1 inch = 5 inches
10 feet = ? feet
If you multiply the numerator by 5, you multiply the denominator by five to ensure the ratio and scale are still accurate and equivalent. 10 * 5 = 50.