A number w with two digits to the right of the decimal point is multip

I thought about that too - I wondered what (incorrect) assumptions they might be making about how math works that could lead them to think C is the right answer here. At first I thought they must be counting any zeros at the end of the product wn (when you do long multiplication using the decimals w and n) as if they were genuine digits. But then there'd be no reason Statement 2 would be relevant; the answer would be A in that case.

I'd be wary about using a source with a question like this, and especially wary about using a source with no answer explanations.

Thank you very much for the reply. I really appreciate it.


For most questions, there actually are answers. Frankly, not for this one. Given that McGraw seems to be one of the general providers, I was hoping most of the prompts would be reliable. I had a similar negative experience with Nova's GMAT prep course (book). Thus, it seems to me that unless it is an official material there are bound to be mistakes. Though some sources are more prone than others. Thus, I try to use 3rd party materials rather as a supplement than a core material.

I marked Answer (E).
Here's my reasoning.

Question gives 'w' as number with two digits to the right of decimal. It can be anything.

Statement 1) Number 'n' has three digits to the right of decimal. If 'w' has odd digits at the extreme right in the digits after decimal and 'n' has any digit other than '0' at the extreme right in the digits after decimal, the decimal places obtained for number 'w*n' are five OR if 'w' has even digits(excluding '0') at the extreme right in the digits after decimal and 'n' has '5' as last digit at the extreme right after decimal the decimal places obtained for number 'w*n' are less than five. INSUFFICIENT.

Statement 2) 'w' has hundredths digit as a non-multiple of 10 i.e. it can be anything other than '0'. AND 'n' has its thousandths digit as a non-multiple of 10 i.e. it can be anything other than '0' but we don't know how many digits are there after decimal in number 'n'. Thus it can have various answer so
INSUFFICIENT.

Together 1) and 2) we know that 'n' has three digits after decimals and third digit is non-multiple of '10' i.e. it can be anything other than '0'. But we don't know the extreme right digit of the number 'w' since if its '2' and number 'n' has third digit as '5' then number 'w*n' would have different decimal places than if 'w' has third digit other than '2' and 'n' has third digit other then '5'.
INSUFFICIENT.

It occurs to me now that they probably want Statement 2 to say that the final digits of n and w are not divisors of 10, rather than "multiples".


Any large book is likely to contain a minor error or two (I've found mistakes in official books too), but there's a difference between a typo that doesn't affect how well you understand the content and a fundamental mathematical error. My books don't contain any mathematical errors (nor any typos I'm aware of), and that is hopefully also true of the books from the most reputable GMAT publishers. You'll find the most realistic practice questions in official books, so relying on them for problems is a good idea, but the official books generally don't do a good job of explain concepts or methods, so you will likely find it worthwhile to find books that do that well.