Qn iscold_cam wrote:8a(1/4)b = ?
(1) b = 1.5a
(2) a = 2
Lets see how do you guys approach this one
8a(1/4)b
= 2ab
A
insuff
B
insuff
A+B
you can solve for A and B
so Ans is C
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A Simple but confusing DS [ 8a(1/4)b = ? ]
Source: Beat The GMAT — Data Sufficiency |
Now the Ans is Acold_cam wrote:Thanks for Quick reply.. but actually the question is
8^a (1/4)^b = ?
(1) b = 1.5a
(2) a = 2
its 8 to the power a and 1/4 to the power b.
I just copied and paste it so there was mistake Sorry
Just simplify in terms of power of 2
you will get your ans
I agree, upon solving we end up with:
8^a.(1/4)^b
2^(3a).2^(-2b)
3a-2b = ?
But isn't is same as the S(1):
b = 1.5a
2b = 3a
and if we further see our original equation 3a-2b = ?
it tells us 3a = 2b which is what the statement (1) is. So is it solving the question.
I know how you will explain this as 3a-2b= 0 so its sufficient but that is exactly the same as question stem.
:roll:
why do we need s(1) to solve it, the question stem is solving it... I think I know why am confused but am still confused lol
8^a.(1/4)^b
2^(3a).2^(-2b)
3a-2b = ?
But isn't is same as the S(1):
b = 1.5a
2b = 3a
and if we further see our original equation 3a-2b = ?
it tells us 3a = 2b which is what the statement (1) is. So is it solving the question.
I know how you will explain this as 3a-2b= 0 so its sufficient but that is exactly the same as question stem.
:roll:
why do we need s(1) to solve it, the question stem is solving it... I think I know why am confused but am still confused lol
1) B = 3/2 A
then,
8^A . (1/4)^(3/2 A) =
=8^A . [(1/64)^A]^(1/2)=
=8^A . [(1/8)^2A]^(1/2)=
=8^A . (1/8)^A=
=1
therefore, Suf
2) we know nothing about B, therefore Insuf
Hence, the answer is A
then,
8^A . (1/4)^(3/2 A) =
=8^A . [(1/64)^A]^(1/2)=
=8^A . [(1/8)^2A]^(1/2)=
=8^A . (1/8)^A=
=1
therefore, Suf
2) we know nothing about B, therefore Insuf
Hence, the answer is A
8^a(1/4)^b = ?
(1) b = 1.5a
(2) a = 2
2^3A * 2^-2B = 4^3A-2B
FROM ONE
2B = 3A THUS 3A-2B = 0 THUS THE EXPRESSION = 1
FROM 2
INSUFF
A
(1) b = 1.5a
(2) a = 2
2^3A * 2^-2B = 4^3A-2B
FROM ONE
2B = 3A THUS 3A-2B = 0 THUS THE EXPRESSION = 1
FROM 2
INSUFF
A
Thanks everyone for your explanations. My biggest problem is with the arithmetic (1/4 ^ 1.5a). So if I take (1^1.5a)(4^-1.5a), how do I get to the next step?
Like msvmuthu explained u still would have to that (3^3a-3a = 2 6 0 =1)
If u do it like u r saying u will get
2^0 * 1 ^ 1.5a
1 raised to any exponent is always 1 so answer is 1
Anyone?
If u do it like u r saying u will get
2^0 * 1 ^ 1.5a
1 raised to any exponent is always 1 so answer is 1
Anyone?
Like msvmuthu explained u still would have to that (2^3a-3a = 2 ^ 0 =1)
If u do it like u r saying u will get
2^0 * 1 ^ 1.5a
1 raised to any exponent is always 1 so answer is 1
Anyone?
If u do it like u r saying u will get
2^0 * 1 ^ 1.5a
1 raised to any exponent is always 1 so answer is 1
Anyone?
its A.. exactly the way muthu explained...cramya wrote:Like msvmuthu explained u still would have to that (2^3a-3a = 2 ^ 0 =1)
If u do it like u r saying u will get
2^0 * 1 ^ 1.5a
1 raised to any exponent is always 1 so answer is 1
Anyone?
I dunno if its easier , but 1.5 = 3/2 and (1/4)^3/2 is cube of square root of 1/4 that is 1/8 so we have 8^a * ( 1/ 8 )^a which is 1^a = 1
