Question 326925
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First give me your address.  I need to get hold of you and wash your mouth out with soap if you ever say "cross cancel" again in your life.


You do NOT cross cancel.  Go back and find the teacher that first taught you to use the terminology "cross cancel" and ask for your money back, or at least for your parent's property tax money back.  That sort of nonsense confuses people and causes more errors than it was ever worth.

You eliminate factors common to both numerator and denominator.


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \frac{2m^2}{s}\ \div\ \frac{4m}{3n}]


Invert and multiply:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \frac{2m^2}{s}\ \times\ \frac{3n}{4m}\ =\ \frac{2\,\cdot\,m\,\cdot\,m}{s}\ \times\ \frac{3n}{2\,\cdot\,2\,\cdot\,m}]


Notice that you have two factors of *[tex \Large m] in the numerator and one factor of *[tex \Large m] in the denominator.  Eliminate one of the factors of *[tex \Large m] in each of the numerator and denominator, leaving one factor of *[tex \Large m] in the numerator.  Likewise the denominator has two 2s and the numerator has one 2...


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \frac{2\,\cdot\,m\,\cdot\,m}{s}\ \times\ \frac{3n}{2\,\cdot\,2\,\cdot\,m}\ =\ \frac{m}{s}\ \times\ \frac{3n}{2}]


Now it is just numerator times numerator and denominator times denominator:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \frac{m}{s}\ \times\ \frac{3n}{2}\ =\ \frac{3nm}{2s}]


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \frac{3nm}{2s}]


is absolutely right and in absolutely simplest form.


Now, it is possible, if you are doing an on line course and having to type your answer in a little box through your school's on-line system, that the system expects to see *[tex \Large \frac{3mn}{2s}] and is scoring your answer as incorrect because the variables are out of order.  You might try to submit that way.  If that turns out to be the case, give me your instructor's e-mail address.  S/he will get a message from me, all caps in a huge red font that says "Commutative Property, Duh!"  One other possibility is that you might need to use some parentheses.  If you just type 3mn/2s, technically what you have written is *[tex \Large 3m\frac{n}{2}s] which is clearly incorrect.  Your system may be expecting to see (3nm)/(2s) or (3mn)/(2s) -- try that.


John
*[tex \LARGE e^{i\pi} + 1 = 0]
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