hariharakarthi's reasoning is correct.
Sometimes algebra word problems are actually testing number property concepts such as factors, multiples, remainders, etc.
It must be true that any number of people is a positive integer. (We can't have a negative or fractional number of people!)
If we let the number of car-owining students be "C" we know that 42% of C is the number of women who own cars:
0.42 * C = number of women who own cars
But, we know that the number of people who own cars (C) must be a positive integer, and we know that the number of women who own cars must also be a positive integer. Therefore:
42% of a positive integer is a positive integer
.42 * pos integer = pos integer
42/100 * pos integer = pos integer
21/50 * pos integer = pos integer
21 and 50 do not share any prime factors; we cannot simplify the fraction any further. Accordingly, in order for the equation to hold true, the positive integer on the left (which was C) must be able to divide 50--it must be a positive multiple of 50.
If the positive integer on the left hand side were not a positive multiple of 50, then the left hand side of the equation would be a noninteger, and would no longer be equal to the right hand side of the equation. But, obviously and by definition, the two sides of an equation must equal each other. So, we know that C is a positive multiple of 50. The question stem necessitates that C<=80. Therefore, C = 50.
The second statement is independently sufficient while the first statement is not.
Choose B.
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