You can also do this without making a common demoninator. If the numbers were increased to i.e something like 15234/15235 and 15676/15677, finding the common denominator would be reduntant and be extremely time confusing. Instead, we can notice that both the fractions are 1/n away from 1. 1/5 is clearly greater than 1/7, as spliting the same thing into 5 things compared to 7 things, is clearly greater. Thus, we are subtracting 1/5 from 4/5, SOMETHING THAT is greater than subtracting 1/7, so therefore 6/7 is greater .
