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But the answer is E and i Cant figure out why and how?? please explian

When you divide both sides of an equation by a variable, you have to exclude the possibility that the variable is equal to zero.

In both 1 and 2, you divide by a variable. This means that the results hold true PROVIDED a and b are not zero. However, in both 1 and 2 would be true if a and b were zero, but ab is equal to zero, not 1. Hence, E is the answer.
_________________

Best,

AkamaiBrah Former Senior Instructor, Manhattan GMAT and VeritasPrep Vice President, Midtown NYC Investment Bank, Structured Finance IT MFE, Haas School of Business, UC Berkeley, Class of 2005 MBA, Anderson School of Management, UCLA, Class of 1993

boss its not clear, please explain this"However, in both 1 and 2 would be true if a and b were zero, but ab is equal to zero, not 1. Hence, E is the answer"
incase we are dividing both sides by a or b then and b are not 0 also ab is not 0? am i right.
Sorry boss but this is my weak area. i loved doing ur C&P problems, it really helped me clear my fundamentals.

boss its not clear, please explain this"However, in both 1 and 2 would be true if a and b were zero, but ab is equal to zero, not 1. Hence, E is the answer" incase we are dividing both sides by a or b then and b are not 0 also ab is not 0? am i right. Sorry boss but this is my weak area. i loved doing ur C&P problems, it really helped me clear my fundamentals.

The question is: Is ab = 1?

If a and b are not zero and 1 and 2 are true, then ab = 1
If a and b are zero, 1 and 2 are still true, but ab = 0.

Hence, we cannot determine whether ab = 1 simple based on whether 1 and 2 together are true.
_________________

Best,

AkamaiBrah Former Senior Instructor, Manhattan GMAT and VeritasPrep Vice President, Midtown NYC Investment Bank, Structured Finance IT MFE, Haas School of Business, UC Berkeley, Class of 2005 MBA, Anderson School of Management, UCLA, Class of 1993