how about we put the fractions into decimals?
1/2 is 0.5
2/3 is 0.66666(6)
So we need to find something that is between them.
the denominator can't be 2, because bigger than 1/2 is 2/2, which is 1 and is bigger than 0.6
it also can't be 3, because smaller than 2/3 is 1/2, which is 0.333... and is smaller than 0.5.
Can it be 4? we can't have 2/4 (it's the same as 1/2), or 3/4, it's 0.75, and it's bigger than 0.666...
how about 5?
2/5=0.4,no, too small
3/5=0.6- perfect! that's the answer!