7/8<span> already reduced to lowest terms, numerator and denominator have no common prime factors, their prime factorization: </span> 7 is a prime number and 8 = 23; 19/20<span> already reduced to lowest terms, numerator and denominator have no common prime factors, their prime factorization: </span> 19 is a prime number and 20 = 2^2<span> * 5; (and if you solve it up you'll see for yourself that its 19/20) </span> So 19/20 is bigger.