The table attached shows the result of survey of 100 students who responded with “For” or “Against” or “Not sure” when asked about the Debate choice of the Topic A and Topic B. What was the number of students who responded “For” for both Topics?

(1) The number of students who did not respond “For” for either Topic was 40.
(2) The number of students who responded “Against” for both Topics was 20.
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Bunuel but the first statement could be solved by the unknown multiplier and a ratio strategy ?? I came to A with this logic or is wrong ??

Thanks
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because you have (make the things simple) FOR 3x + 7x = 100 so your UM is 7x (70 of bunuel): with 7x we have not real number but 1) provide us with.

IF 7x is the total number of students AND 40 not respond so 60 respond. IF you have 7x = 60 (real number) you CAN calculate the number of student (remember: we are talking of integers, so even you have 14.5 is not possible, is a constraint not written but you have to take in account for). However, it depens a lot from the context.

\(BE careful\): this is totally an inference and intuitive approach, that come up after several time of study and that you develope instinctively. Similar native speakers have about SC
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expand the tablet will lead fast and direct solution:

For only For both||| Against only Against both||| Not sure for only Not sure for neither|||

A 30-x x 40-y y 30-z z

B 40-x x 20-y y 40-z z

now it's very graphic:

the question is x=?

(1) not for either is 100-(30-x+x+40-x)=40

sufficient

(2) y=20

insufficient