In NFER 11c q14 you are asked to find the largest out of 7/8 3/4 6/9 10/12 3/5. I can not see a common denominatorfor for all these numbers, and converting all of them to decimal could be time consuming in an exam. Has anyone has a really quick way to compare these fractions?
System I used with DD. Will vary slightly depending on numbers and whether you are, for example, after biggest or smallest.
For the numbers you give.
Eliminate the smallest numbers.
Do this by looking for those numbers bigger than, say 1/2 or 3/4. 3/4 would seem to be the better choice. 7/8 and 10/12 are obviously bigger than 3/4. Straightaway down to two numbers.
After the biggest of the remaining two numbers.
Both numbers are smaller than 1, so compare and determine how close.
7/8 is 1/8 away, and 10/12 is 2/12 or 1/6 away. 1/8 is the smallest number, so 7/8 is closest to 1 and therefore biggest number.
The method looks a bit long-winded, but in practice, providing child has a reasonable grasp of equivalent fractions, only takes a few seconds, and does not involve any writing down.