Set TWo Q17

[wvspidermonkey]

Q17:
If a and b are positive, is (a-1 + b-1)-1 less than (a-1b-1)-1?

(1) a = 2b
(2) a + b > 1

Formal Answer: E

My answer:
(1) The value of b can be determined and substituted into the original equation to find an answer.

See attachment for graph of answer 1.

(2) a+b>1 does not give enough information. Either letter could be negative with the other number being a larger positive number. By multiplying the letters, I can’t be sure if the answer would be positive of negative.

I think the answer is A.

[kevin]

Try simpliying the question : Is ab/(a+b) < ab i.e. is a + b > 1 ?

Remember that a and b are positive!

[wvspidermonkey]

I'll review this again tonight.

Thank you!
A

[lerckin]

(a-1 + b-1)-1 < (a-1b-1)-1 only If :

a + b-3 < a-b-2
a + b - 3 -a + b+ <0
2b - 1 < 0
2b < 1
b<0.5

So :

(a-1 + b-1)-1 < (a-1b-1)-1 only if b<0.5

Neither (1) nor (2) can help to find b

so E is correct