Use the number line to determine whether the two fractions 1/2, 4/8 are equivalent. yes or no.

You could do that (yes), but in many cases, you would need to determine equivalence some other way (no) before plotting the numbers on a number line.

If the number line is graduated in a manner that makes 1/2 clear, and also makes 4/8 clear, then it is possible to determine that both values lie at the same point. If the number line is graduated in tenths or hundredths (for example), you would need to convert both numbers to that format before plotting.