21/42 = 50%
A fraction like 21/42 shows up when half of something is used, chosen, or completed. For example, if 21 out of 42 students bring lunch from home, that group represents 50% of the class.
You can picture 21/42 as one whole split into two equal parts, with one part shaded. A quick estimate is to recognize that the numerator is half of the denominator, so the value is exactly halfway, or 50%.
A common mistake is thinking that 21/42 is a large fraction because both numbers are fairly big. The actual size depends on their relationship, and since the top number is half the bottom number, the fraction is not more than one-half.
