In the big Book p.g 450 (Fractions and Decimals) Question 16

[dddannie6]

Hi,

So I am looking at question# 16 on Chapter 11 (Fractions and Decimals)

The question reads as follow:
xy does not equal 0

Quantity A Quantity B

2+ (1/xy) [(2xy)+ 1]/xy


Now the answer written to this question is C. According to the answer explanation everything cancels out to show that they are equal. However, I am uncomfortable with this answer because (1) I don't understand how 2(xy)/(xy) can just cancel out to be 2 and (2) because considering how the answer does not specify that x or y cannot be negative if I say plug in -1 for x and 5 for y, I do end up with Quantity A equaling (-8)/10 and Quantity B equaling to 9/5.

However, if I change the sign of the values for both x and y to be both positive then Quantity A becomes 12/10 and Quantity B becomes 11/5. Either way the answer for this question does not end up being option C.


Am I missing something?

-Dannialles D

[tommywallach]

Hey Ddanie,

I wrote a response to this, but it looks like it disappeared or something. Sorry about that.

Two things -- the cancellation is just how math works, so I don't quite know what to say to that (anything that's in the numerator and the denominator can cancel, and anything that's in both column A and column B can cancel, assuming you aren't dividing or multiplying by a negative number in so doing).

To the other issue, I double-checked the math, and you did your arithmetic wrong. The two columns always end up equal, whatever you plug in.

-t