adkikani wrote:
DavidTutorexamPAL nick1816 VeritasKarishma MentorTutoringQuote:
What was the population of City X in 2002 ?
(1) X's population in 2002 increased by 2 percent, or 20,000 people, over 2001.
(2) In 2001, X's population was 1,000,000.
Could you advise what is incorrect in below approach:
St 1:
X's population in 2002 increased by 2 percent over 2001. -> P(2001) * 1.02 = P(2002)
i.e.
X's population in 2002 increased by 20,000 people over 2001. -> P (2002) = P (2001) + 20,000
Suff.
Unfortunately, hurriedly I too selected C with this thought:
To find a final value, I need initial value and change of %tage or difference hence I need to use St 2.
I could not form two linear eqs of (1) under timed conditions.
Hello,
adkikani. Keep in mind that with DS questions in particular, you often do not need to actually
solve the problem to answer the question. Here, we are asked about an
exact value of a population at a specific point in time: we need
to be able to determine
the population of City X in 2002, nothing more. A quick scan of the two statements reveals that they both provide information on 2001, so STOP. Ask yourself, what would we need to know about 2001 to determine the population for 2002? Either a rate of growth with some sort of total attached or a difference in the total number of people, as long as you had a baseline population, would do. Now you can assess the statements. I like to start with the easier looking of the two, so I would pick (2) first.
Clearly, Statement (2) does not deliver on our pre-thinking for the problem. We get a population from the year before, but nothing more. With no basis for comparison, we cannot predict what happened the next year. Mark off (B) and (D) as answer choices. How about Statement (1)?
Aha. If 2 percent corresponds to 20,000 people, and you understand that there was a growth or
increase in population, then you
could calculate the population in either 2001 or 2002. Note that without the word
increased, the change would be unknown, whether the population had gone up or down, and the answer would be insufficient. As is, however, you could work out pretty quickly that 1 percent of
1,000,000 is 10,000 just by moving the decimal two places to the left, so two 1 percents would be 2 * 10,000, or 20,000 people. Thus, the original population was 1,000,000, and we know that Statement (1) is SUFFICIENT. The answer is (A).
I did not do anything more than solve this one through reasoning. Whenever you encounter DS problems, always ask yourself three things:
1) What is the question asking?
2) What do I know? (i.e. What information is provided?)
3) What would I
need to know to answer the question that is being asked?
Such an approach can spare you all the work sometimes, and you will be less prone to falling into traps. I hope this may help you in your studies.
- Andrew