The tricks used in Data Sufficiency
questions come from a narrow pool of tricks. Learn to identify
each of the tricks, and you will be in a strong position to answer
each question. In approaching each question, apply the three
step method we discussed earlier:
Step (1) Look at the question stem.
Step (2) Look at each statement individually.
Step (3) Then look at both statements in combination.
It is important that you have the
discipline to stick to this approach. The Data Sufficiency questions
tend to be trick questions, particularly the difficult ones,
and straying from this basic strategy will increase the chances
of you being fooled.
Remember
that standardized tests are based on the premise that you can
separate students into groups of ability. In order to do this,
the less capable students must get questions wrong. To make sure
less capable students get low scores, the tests are deliberately
designed with trick questions specifically made to fool you.
Selected Trick Questions
AMNESIA TRICK
How many adults ride bicycles in city A if all adults in City
A either ride bicycles or drive cars?
(1) 85% of the 10,000 adults in city A drive cars.
(2) 8500 adults in city A drive cars.
(A) Statement (1) is sufficient
since if 8,500 drive cars then 1,500 ride bicycles. Statement
(2) is not sufficient since we do not know the total population;
it cannot be assumed from (1).
The
trick here is that 1 alone can answer the question. Although
1 and 2 together may answer the question, the answer is still
A. The unskilled reader will carry over the information from
statement 1 when reading statement 2 and not catch the flaw with
statement 2 (it does not tell you the population). Trick #2:
note that the question doesn't tell you the total population
of City A, but the total population is not relevant since the
question only asks for "Adults".
This
question shows how you must have discipline and stick to the
3 step process.
(1) Read the stem
(2) Read each statement individually
(3) If both statements cannot answer the question alone, then
look at both statements together. Before you try to combine
statement 1 and 2, make sure each answer can/cannot answer the
question. When you first read statement 2, temporarily forget
what you read in statement 1 so that you may evaluate if (2)
alone is sufficient. Hence the name of the trick question: "Amnesia."
Get temporary amnesia after reading statement 1 and don't use
statement 1's information when you first evaluate statement 2
(because you need to see if statement 2 is sufficient alone.
DELAY TRICK
How much was a certain Babe Ruth baseball card worth in January
1991?
(1) In January 1997 the card was worth $100,000.
(2) Over the ten years 1987-1997, the card steadily increased
in value by 10% each 12 months.
(1) alone is obviously insufficient.
To use (2) you need to know what the card was worth at some time
between 1987 and 1997. So (2) alone is insufficient, but by using
(1) and (2) together you can figure out the worth of the baseball
card in January 1991. The trick here is not to do the calculations.
If you tried to actually calculate the value in January 1991,
you have fallen into the trap. All that matters is that sufficient
information is available.
The test designers make these
questions to make you waste time so that you do not finish the
test on time. This is called the DELAY trick because it causes
you to be delayed and lose valuable time if you do unnecessary
calculations.
BACKSOLVE
Is the two-digit integer, with digits r (first) and m(second),
a multiple of 7?
(1) r + m = 13
(2) r is divisible by 3
With statements 1 and 2 we may
determine that the two digit number is not a multiple of 7. Using
statement (1) Try all the two digit numbers that sum 13: 94,
85, 76, 67, 58, 49. Of those, only 49 is divisible by 7. So,
using statement 1, rm may or may not be a multiple of
7; it is insufficient. (2) Is not sufficient because there are
many numbers with r that are divisible by 3 and that are
multiples of 7 (35, 63, 98). Combined, there are NO possible
numbers rm that are divisible by 7 and satisfy statements
1 and 2. The answer is NO, rm is not a multiple of 7.
Using statements 1 and 2 we may deduce this.
Using statement 2, however, 49 is not a multiple of 3. So, combining
the two statements proves that rm is not a multiple
of 7. In other words, we've used the two statements to deduce
that rm is not a multiple of 7.
This looks like a very intimidating question. As a rule, when
you encounter a highly intimidating question such as this one,
you should plug in possible answers. This question defies an
algebraic solution, so it must be solved through backsolving.
RED HERRING
TRICK
Billy sells twice as many $20 tickets as Tim, and Tim sells three
times as many $10 tickets as Billy. How many tickets did Billy
sell? Tickets are either $10 or $20.
(1) Tim sold a total of 35 tickets
(2) Together Billy and Tim sold 70 tickets for $1000
1 is not sufficient. Let x =
the number of $20 tickets sold by Tim and y = the number of $10
tickets sold by Billy. Then
Billy sold 2x ($20 tickets) + y ($10 tickets)
Tim sold x ($20 tickets) + 3y ($10 tickets)
(2) implies 70 = x + 2x + y + 3y and 1000 = 20(x + 2x) + 10 (y
+ 3y)- divide this equation by 20 to simplify. Subtract these
two equations
70 = 3x + 4y
-50 = -3x - 2y
20 = 2y may be solved for x and y and subsequently y = 10 and
x = 10, Billy sold 2(10) + 10 = 30 tickets.
The trick here is that 1 is completely unnecessary and a distraction.
The information in 1 may help answer the question, but it is
unnecessary; 2 can do it alone.
International
students: A "red herring" is an American/English phrase
for something that is a distraction to the issue. In this case,
the first statement is a distraction.
SUPER STATEMENT
TRICK
What is the average (arithmetic mean) of 3x and 12z?
(1) x + 4z = 20
(2) x + z = 8
Yes, combining A and B will solve
the question, but A can do it alone. The trap is C. Students
will know that the two statements together can solve the question.
SUPER
STATEMENT questions involve
questions where together both statements can solve a question,
but carefully examined, one statement may solve it alone.
The given information asks for the average of 3x and 12z, which
is (3x + 12z) / 2, or 3(x + 4z)/2. Statement 1 tells us the value
of x + 4z, (x + 4z)/3. So you can solve the average formula directly
without using the second statement. x + 4z = 20, so 3x + 12z
= 60, meaning that the average = 30. You may use statement 2
to solve the problem, but statement 1 can do it itself (thus
disqualifying choice C, which requires both 1 and 2 to be insufficient).
HINT: on difficult Data Sufficiency questions,
the statements usually have more value than it appears at first
glance.
