# Homework problem

1. Jan 27, 2010

### Cornraker

1. The problem statement, all variables and given/known data

Express the number in the form a/b

2. Relevant equations

$$-2^{4} + 3^{-1}$$

3. The attempt at a solution

16+(-3) = 13

Why is this not the correct answer?

2. Jan 27, 2010

### sara_87

1) should the negative sign in the term -2^4 be inside the bracket? should it be (-2)^4? If yes then 16 is correct.

2) for any number, say x, x^(-1)=1/x not -x.

can you do it now?

3. Jan 27, 2010

### Cornraker

Well if the negative sign is outside as such: -(2^4), does that make it a -16 instead of positive?

4. Jan 27, 2010

### sara_87

yes.

so what do you get for the answer?

5. Jan 27, 2010

### Staff: Mentor

Yes, as opposed to (-2)4, which is 16.

Both what you have written, -(24), and -24 are equal to -16.

6. Jan 27, 2010

### Cornraker

47/3.

After you told me 3^-1 was not -3 but instead 1/3, i was able to figure it out. I cross multiplied -16 with 1/3 and i came out with 48 then when i added the fraction i came out with 47/3. does it sound right?

7. Jan 27, 2010

### sara_87

you cross multiplied??

you just have to add -16 to 1/3.

I think you have the answer...you just forgot a minus sign...right? ;)

8. Jan 27, 2010

### Cornraker

This problem is giving me trouble. The correct answer is 47/3. I just can't figure out how to arrive at it. I thought i could arrive by cross multiplying, but looking at it again, it doesnt seem right.

9. Jan 27, 2010

### Staff: Mentor

Are you sure you have given us the problem verbatim? The answer to the problem you posted is -47/3, not 47/3.

-24 + 3-1 = -16 + 1/3 = -48/3 + 1/3 = -47/3

To get a common denominator of 3, you multiply -16 by 1 (in the form of 3/3) to get -48/3. Now both denominators are 3 and you can add the numerators.

10. Jan 27, 2010

### Cornraker

Yes sorry i meant to say -47/3. I wasnt sure how you arrived at -48/3 but i realize i forgot about finding the common denominator

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