16/64 = 1/4 when you divide the numerator and denominator by 16.
16 ÷ 16 = 1
64 ÷ 16 4
Note that 16/16 is 1 and when you divide by one the number does not change. In fractions they may look different 16/64 does not look like 1/4, but they are worth the same. Getting 16 questions wrong on a test with 64 items means you got 1/4 of the test wrong.