Is ab = 32? I. a = sqrt64 II. (a - 8)(b - 4) = 0

Question

Is ab = 32?

I. a = sqrt64
II. (a - 8)(b - 4) = 0

duttsit · Answer

E.

S1 gives a = +/- 8 insufficient
S2 givs, a =8 OR b = 4 OR both

together they give: a = 8 but no info about b. insuffucient

HIMALAYA · Answer

from i, a = 8
from ii, b could be 4 or anything because (a-8) = 0. so E.

hkm_gmat · Answer

any reason why it should not be B ?

SunShine · Answer

One more vote for E.


B could not be the answer because: if a=8, b can be any value,
and therefore can or can not be ab=32 and so insufficient, 
alternatively if b=4, a could be any value so ab can be or can not be 32.

so ab=32 can be or can not be true. there no a difinite answer that ab=32!

lhotseface · Answer

Himalaya makes an important point..for the GMAT the square root has only one ( positive ) answer. I had also forgotten..thanks. :!:

ywilfred · Answer

1) a = 8 or -8. Not sure what b is. Insufficient.

2) Three ways: a = 8, b = 4, or a=8 and b =4. Not sure which combination, so insufficient.

Using (1) and (2), not sure what a is. b could be 4 in which case value of a is of no consequence.

Ans E

ps_dahiya · Answer

Statement 2 has two possibilities

1. a = 8, b = anything
2. a = anything, b = 4

So we don't know what can is the product of a and b.

Hope this helps...

jinesh · Answer

Hi Dahiya...... u mentioned 2 possibilities...but ....its 3 rite?? 1. a = 8, b = anything 2. a = anything, b = 4 3. a= 8 & b=4 and so we are not sure which of the 3 combination is correct !!!??? And again.....according to Himalaya ... In GMAT the square root has only one ( positive ) answer so in ST1 --> sqrt(64) = 8.... ST2 --> 1. a = 8, b = anything 2. a = anything, b = 4 3.a= 8 & b=4 so 1& 2 give a = 8 and so b= 4 ?? so is it C????? correct me if I am wrong... :oops:

Jinesh

ps_dahiya · Answer

IMO 3rd possibility is covered in the first two. So, infact, 3rd is not a seperate possibility. Thats why I chose E.

This is my understanding. I may be wrong. Lets wait for OA and OE.

jinesh · Answer

hmm...

Mere "BHAI" wats the OA??? I like ur nick yaar...

GMATT73 · Answer

I concur with E. 

1. A=8, but we don`t know B. Insuff.
2. A can be 8 and B can be anything.
<or> A can be anything and B can be 4. Insuff.

together, B can still be anything.

old_dream_1976 · Answer

Himalaya Please confirm why is a= 8 as against a = =/-8 Does GMAT reallt consider only +ve roots? I did not know this. :shock:

allabout · Answer

The square root of a negative number is undefined. You can't take the square root of a negative number.

eleni24 · Answer

I can't understand why "a" cannot be -8...It says that "a" is the square root of 64...It doesn't say "what is the square root of -64" (which is undefined).
It says that "a" is a number that becomes 64 when you square it...There are two numbers which become 64 when you square them: 8 (8*8=64)
and -8 (-8 * -8=64).Why can't a be -8?

ywilfred · Answer

For this case, a can be 8 or -8. Why statement is written off is because you have no knowledge of what the value of b is.

Is ab = 32? I. a = sqrt64 II. (a - 8)(b - 4) = 0

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