Bunuel wrote:
If m < 15 and m > –4, which of the following must be true?
A. m > –15
B. m < 4
C. m > 4
D. –4 < m < 4
E. –15 < m < 4
We note that since m is greater than -4, any possible value of m will also be greater than -15, therefore m > -15.
To see why other choices are not possible, let’s pick values for m close to upper and lower bounds, such as m = -3 and m = 14.
Answer Choice B: We see that m < 4 is not necessarily true since m can equal 14.
Answer Choice C: We see that m > 4 is not necessarily true since m can equal -3.
Answer Choice D: We see that -4 < m < 4 is not necessarily true since m can equal 14.
Answer Choice E: We see that -15 < m < 4 is not necessarily true since m can equal 14.
Answer: A
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