1/10 is missing as if u turn all the other fractions into decimals u will see that they all equal to 0.9 so the last bit must be 0.1 which is 1/10
u can also add the fractions
so u have to change the denominator so that all their denominator is the same using the cross method
1/3 +1/6
6/18+3/18
=9/18
=1/2
1/2+2/5
=5/10+4/10
=9/10
So the missing part is 1/10
