Which of these fractions is the largest - 33/56 ,4/7, 9/21, 6/14

As it is not clear which is biggest, we need to make sure that the fractions are in their simplest form. For 33/56 there no common factors so this is the simplest form. 4/7 is clearly in the simplest form. 9 and 21 have a common factor of 3, so take this out and we get 3/7. 6/14 has a common factor of 2 and so taking this out we get 3/7. Already we can see that 4/7 is bigger than 9/21 and 6/14 so we just need to compare 33/56 and 4/7. To get these fractions to have the same denominator, the easiest way is to multiply by the highest common factor. Using knowledge however that 56 = 7 x 8, I can multiply 4/7 by 8/8 to get 32/56. Thus seeing that 33/56 is the biggest fraction.