The toss resulted in an odd number

Let Event A : toss resulted in an odd number Event B : number is less than 4

Therefore $A={ 1,3,5}$ i.e. $p(A)=3/6=1/2$ $B={1,2,3}$ (A complement(Π) B) = {1,3} therefore $p(AΠB)$ = $2/6=1/3$ required probability p(number is less than 4 given that it is odd) = p(B/A) = probability of odd number/probability of event $A =1/3×2/1=2/3$

Since it is given that the result is odd there are 3 possible outcomes: 1,3 or 5. Since only 1 and 3 are less then 4 the answer is 2/3.