# Sat prep help

1. Sep 11, 2008

### boricua_2004

1/(1/a)-(1/b) a cannot = 0 b cannot equal= 0 and a cannot equal b

i would gladly appreciate if someone can help me

2. Sep 11, 2008

### rocomath

Ok ... so what is the problem asking?

3. Sep 11, 2008

### boricua_2004

just asking to simplify the problem

4. Sep 11, 2008

### rocomath

$$\frac{1}{\frac{1}{a}}-\frac{1}{b}$$

Multiply the numerator of 1/(1/a) by a and the denominator (1/a) by a.

Also, next time post this in the Precalculus section.

5. Sep 11, 2008

### boricua_2004

is that wat you think it is or the answer and how did you get there and from my answer choices thats not one them

6. Sep 11, 2008

### rocomath

I'm not going to do it for you.

Continue working it with what I suggested with my other reply.

7. Sep 11, 2008

### boricua_2004

ok no prob

8. Sep 11, 2008

### boricua_2004

ok i have this so far a-1/b im i in the right path

9. Sep 11, 2008

### rocomath

Good!

So what is the requirement to add fractions? What do you need in common?

10. Sep 11, 2008

### boricua_2004

a denominator if im correct

11. Sep 11, 2008

### rocomath

Yep. So a's denominator is just 1, so 1/b determines the denominator needed.

Multiply a's numerator and denominator by what number or letter?

12. Sep 11, 2008

### boricua_2004

multiply by b

13. Sep 11, 2008

### rocomath

So what do you get?

14. Sep 11, 2008

### boricua_2004

b-a please tell me im correct

15. Sep 11, 2008

### boricua_2004

because if i multiply by b the b cancels in the denominator and then its a-b or b-a right

16. Sep 11, 2008

### rocomath

No, you're only multiplying a by b and writing all of the numerator under a common denominator, b.

Ex:

$$1-\frac{1}{2}=1\cdot\frac{2}{2}-\frac{1}{2}=\frac{2-1}{2}$$

17. Sep 11, 2008

### boricua_2004

so it should equal ab-1/b

18. Sep 11, 2008

### rocomath

Be careful with how you write or type it.

Is that $$ab-\frac{1}{b}$$ or $$\frac{ab-1}{b}$$???

19. Sep 11, 2008

### boricua_2004

ab-1
b

20. Sep 11, 2008

### boricua_2004

ab-1/b
the second one