If n and k are integers whose product is 400, which of the following statements must be true?
(A) n + k > 0 Not necessary e.g. -20 and -20
(B) n neq k Not Necessary e.g. 20 and 20
(C) Either n or k is a multiple of 10. Not necessary. e.g. 25 and 16
(D) If n is even, then k is odd. Not necessary. e.g. 20 and 20
(E) If n is odd , then k is even TRUE. 5 and 80. 25 and 16.

D and E are not same. For D you need to find an even no first and evaluate the second statement.

For E, you need to find an odd no first and then evaluate the second statement. If first no is odd second no will be always even.

When i took a course a while back, well two yrs back the instuructor mentioend that for WHICH OF THE FOLLOWING QUESTIONS, if you are in a rush, pick D or E. They are more likely to be correct. Not saying you should use this, but start with these two option, your chances improve especially when u dont have time.