Why 3/6 is not equivalent to 2/9

Because 3/6 equals 1/2 and 2/9 equals 1/3

3/6 simplified is 1/2. To compare the fractions, you multiply the fractions to get the least common multiple, which in this case is 18 (2 x 9 is 18.) I would multiply 1/2 times 9, which would be 9/18. I would then multiply 2/9 by 2 to get the bottom number to 18, which would be 4/18. You can see that 4/18 and 9/18 are not the same. This is why they are not equivalent.