MikeMighty wrote:
Great explanation as always. However, I approached it differently.
\(m^3 + 380 = 381m\)
\(m(m^2-381)=-380\) then \(m^2-380=\frac{-380}{m}\)
next \(m^2=381-\frac{380}{m}\), and now we plug in the answer choices and
only (C) -19 gives us the right answerWhat do you think
Bunuel?
Hi Mike,
I would like to highlight that the correct answer is B not C. The right answer is -20.
I did the same like you till a point and used other reasoning. Usign sense of numbers and memorizing some square of integers a re perfect. I will elaborate.
\(m(m^2-381)=-380\).........I need two numbers that gives -380
m^2 can't me less than or equal to 381 otherwise, it will be as follows:
Case 1:Negative (
Positive less 381 - 381) = positive value .......Incorrect
Case 2:Negative (
Positive equal to 381 - 381) = 0 .......Incorrect
D) -1
This will give you case 1......Eliminate D
C ) -19
m^2 = 381...So it is case 2.....Eliminate C
B) -20
-20 ( 400 -381)= -20 * 19 = -380.........Correct
Answer B