Fractions, Decimals, %'s Question

[ssiptrott]

Can anyone provide some color on this question...not sure if I completely follow the logic of the explanation? I would have thought the answer is 'Both statements together are sufficient'. Can you not assume that each weekday has an equal weighting (i.e 52 Mondays in a year, 52 Tuesdays, etc.) Thanks

In year x, it rained on 40% of all Mondays and 20% of all Tuesdays. On what percentage of all the weekdays in year x did it NOT rain?
(1) During year x, it rained on 10% of all Wednesdays.

(2) During year x, it did not rain on 70% of Thursdays and it did not rain on 95% of all Fridays.

Answer & Explanation: (1) AND (2) INSUFFICIENT: Both statements together, in conjunction with the information given in the question, provide the annual rain percentages for each weekday during year x. However, because we do not know the proportion each weekday represents relative to the total number of weekdays in year x, we still do not have sufficient information to answer the question.

[jnelson0612]

Sure! Let's think about this. There are 365 days in a year. If you divide that by 7 days in a week, you get 52 weeks and 1 day in each year.

If a year starts on a Sunday, you go through 52 weeks of Sundays through Saturdays and your one extra day falls on a Sunday. So you have 52 Mondays, Tuesdays, Wednesdays, Thursdays, and Fridays.

However, if the year starts on a Monday, your extra day falls on a Monday. Thus, you have 53 Mondays, but only 52 Tuesdays, Wednesdays, Thursdays, and Fridays.

I hope this makes more sense!

[LucasM827]

Would the one extra day, out of 365, even be enough to change one of the percents? It doesn't say "what percentage, down to the thousandth"? It seems ridiculous that the answer isn't "C."

[Sage Pearce-Higgins]

I agree that this question seems quite pedantic. However, the trap is a good one: thinking "wait, can I assume that we've got the same number of each weekday in a year?" is exactly the kind of thinking we need for GMAT.

If a DS problem asks for a numerical answer, a statement is sufficient if the statement gives exactly only one possible answer. It doesn't matter how close the alternative answers are. I can think of some Official Guide problems that hinge on a difference of thousandths, for example DS282 from OG2020.