Question

How many fractions are equivalent to 4/5.Explain

Answer 1

There are an infinite number of them. 

Pick any number, multiply the 4 and the 5 both by it, and write the new
numbers in place of them.  The new fraction is equivalent to  4/5 .

Instead of reducing a fraction to lower terms, what you have just done is
expand the fraction to higher terms. 

Answer 2

infinite, there are an infinite amount of numbers lol