narisipalli wrote:
If x is an integer and x not = 0, is x^4 < 90?
1) \(x^{\sqrt{4}}<10\)
2) \(\frac{2}{x^4} >0.2\)
My answer was
but the original answer is
.
Here is the explaination given for the correct answer -
This is a yes/no problem, so you should plug in. Since , you can rewrite the inequality given in statement 1 as . If x = 3, then , so the answer to the question is "yes." If x = 1, then , so the answer is "yes" again. If x = – 3 then , so the answer to the question is "yes" again, and you should write down AD. For statement 2, if x = 3 then the answer to the question is "yes." If x = 1, then the answer is "yes." If x = – 3, then the answer is "yes" again, so the answer is D.However, I feel that statement 1 is not sufficient given that \sqrt{4} should result in +/-2 and just not +2. If -2 is considered, then x can take any value to be less than 10.
What do you think? Thanks.
Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.
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The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question. We should simplify conditions if necessary.
Since x is an integer, \(4^4 = 256 > 90\) and \(3^4 = 81\), \(x^4 < 90\) is equivalent \(-3 ≤ x ≤ 3\).
Since we have 1 variable (\(x\)) and 0 equations, D is most likely to be the answer. So, we should consider each condition on its own first.
Condition 1)
\(x^\sqrt{4} = x^2 < 10\) tells \(-3 ≤ x ≤ 3\), which is equivalent to the question.
Condition 1) is sufficient.
Condition 2)
\(\frac{2}{x^4} > 0.2\)
\(⇔ \frac{x^4}{2} < \frac{1}{0.2} = 5\)
\(⇔ x^4 < 10\)
\(⇔ -1 ≤ x ≤ 1\), since \(x\) is an integer and \(2^4 = 16\).
In inequality questions, the law “Question is King” tells us that if the solution set of the question includes the solution set of the condition, then the condition is sufficient
Condition 2) is sufficient
Therefore, D is the answer.
If the original condition includes “1 variable”, or “2 variables and 1 equation”, or “3 variables and 2 equations” etc., one more equation is required to answer the question. If each of conditions 1) and 2) provide an additional equation, there is a 59% chance that D is the answer, a 38% chance that A or B is the answer, and a 3% chance that the answer is C or E. Thus, answer D (conditions 1) and 2), when applied separately, are sufficient to answer the question) is most likely, but there may be cases where the answer is A,B,C or E.
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