So 40% of the houses must have exactly one person (100-60 =40)
Now in these houses with one person in them, 35% of them are males
Notice that it is 35% of the 40% of the houses
35% of 40% = 35/100 x 40 = 14%
So we have : 60% of all the houses have 2 or more people
14% of all the houses have one person (male) in them
Therefore * 26% of the houses have one person (female) in them
Look carefully at the question you are asked:
Of all the houses what percentage have exactly one female and no male.
If there are no males they must be females; but we also require exactly one female in the house. That means there must be one person in the house and that person must be a female. That is exactly the situation in statement *
Hence of all the houses 26% have exactly one female and no male.