What is the value of b? (1) b(b - 8) = -16 (2) (b + 4)^2 = 64

Question

Competition Mode Question

What is the value of b?

(1) b(b - 8) = -16
(2) (b + 4)^2 = 64

suchita2409 · Answer

IMO A.

b(b-8)+16 gives us b= 4.

Suff.

(b+4)^2= 8^2
Gives us 2 values of b:4,-12
Insuff.
A

Posted from my mobile device

RaghavKhanna · Answer

1. b^2 - 8b + 16 = 0
=> (b-4)^2 = 0
=>  b = 4

St. 1 is sufficient.

2. (b+4)^2 = 64
=> b^2 + 16 + 8b = 64
=> b^2 + 8b - 48 = 0
=> b^2 + 12b - 4b - 48 = 0
=> b(b+12) - 4(b+12) = 0
=> (b-4)(b+12) = 0
=> b = 4, -12

St. 2 is insufficient.

Answer: A

harsh61998 · Answer

IMO A.

We are asked what is the value of b.

Statement I:  
We can write b(b-8) = -16 as b^2 - 8b + 16 = 0
This is the same as saying (b - 4)^2 = 0

Therefore, b = 4.

Statement I is  SUFFICIENT .

We can eliminate options  B ,  C  and  E .

Lets look at  Statement II: 
(b + 4)^2 = 64
This is the same as b^2 + 8b - 48 = 0.

From the above equation we get two values of b i.e. 12 and -4.

Therefore Statement II is  INSUFFICIENT.

We can eliminate option  D .

Answer: A

Posted from my mobile device

Manasvi1 · Answer

1) b(b-8) = -16
 => b^2 -8b +16 = 0
 => (b - 4)^2 = 0
 => b = 4
   Sufficient

2) (b + 4)^2 = 64
=> b + 4 =  \sqrt{64} 
=> b + 4 = +8 or -8
=> b = 4 or -12
   Not Sufficient

Hence OA is (A)

v12345 · Answer

Statement 1: 
 b(b - 8) = -16 
 => b^2 - 8b + 16 = 0 
 => (b - 4)^2 = 0 
 => b - 4 = 0 
=> b = 4
Hence, sufficient alone.

Statement 2:
 (b + 4)^2 = 64 
=> b + 4 = 8 or b + 4 = -8
=> b = 4 or b = -12
Hence, insufficient.

Thus, OA is (A).

ccheryn · Answer

(1) b(b - 8) = -16

gives b^2 -8b +16 = 0
(b-4)(b-4) = 0 
gives b =4 sufficent

(2) (b + 4)^2 = 64
(b+4) = +/- 8
b = 4 or -12 so not sufficient

hence A

sambitspm · Answer

Kindly see the attachment.

TIME: 0:58
IMO A

aishhole · Answer

1) b(b-8) = -16
this equation gives two identical solutions for b. SUFFICIENT

2) (b+4)^2 = 64 
==> (b+4) = +/- 8
This equation gives two solutions for b, NOT SUFFICIENT

IMO A

GMATinsight · Answer

Question: b = ?

Statement 1 : b(b - 8) = -16

i.e. b = 4

SUFFICIENT

Statement 2 : (b + 4)^2 = 64

i.e. b+4 = +8 or -8
i.e. b = +4 or -12

NOT SUFFICIENT

Answer: Option A

AbhISB2021 · Answer

Statement 1 is sufficient to answer the question but not statement 2.
From statement 1:
b=4
From statement 2;
b=4 or -8

Posted from my mobile device

AkshayC95 · Answer

Value of b?

Statement 1
b(b-8)=-16
b^2 - 8b = -16
b^2 - 8b +16 = 0
b^2 -4b -4b +16=0
b(b-4) -4(b-4)=0
(b-4)(b-4)=0
b-4=0
b=4. 
We have a value for b which is 4, Let's Hold on to A and move to 2nd Statement.

Statement 2 
(b+4)^2=64
2 ways to go about(What I feel) 
1st way 
(b+4)^2=64
Cancel Square on both sides
(b+4)= Positive8
or 
(b+4)= Negative8
As nothing is specified. Can't say Really

2nd way
Open the square
(b+4)^2=64
b^2+2(b)(4) + 16 = 64
b^2 +8b +16 - 64=0
b^2+8b-48=0
b^2 +12b-4b-48=0
b(b+12)-4(b+12)=0
(b+12)(b-4)=0
b can be -12 or b can be +4
Can't Say Really. Statement 2 Not sufficient.

As statement 1 is only Sufficient ans is Option A.

NiftyNiffler · Answer

What is the value of b?

(1) b(b - 8) = -16
(2) (b + 4)^2 = 64

The answer should be  A

st1) b(b-8) = -16
b^2 - 8b + 16 = 0
=> (b-4)^2 = 0
=> b = 4 (SUFFICIENT)

st2) b+4 = 8 or b+4 = -8 
So b = 4 or -12 (INSUFFICIENT)

minustark · Answer

What is the value of b?

(1) b(b - 8) = -16
(2) (b + 4)^2 = 64

1) b^2 - 8b + 16 =0, or, (b -4)^2 = 0, b = 4. sufficient.

2) b^2 + 8b + 16 -64 = 0, or, b^2 +8b - 48 = 0, or, b^2 +12b -4b -48 =0, or,b(b+12) -4 (b +12) =0, or, (b+12) (b-4)=0. b can be either -12 or 4. not sufficient

A is the answer.

MayankSingh · Answer

IMO A

value of b?

(1) b(b - 8) = -16

b^2 -8b+16 = 0
b^2-4b-4b+16=0
(b-4)(b-4)=0
(b-4)^2=0
b=4 (equal roots) 
  Sufficient

(2) (b + 4)^2 = 64

(b + 4)^2 = 64
(b + 4) = ± 8
b= -4 ± 8
b= -12 0r b=4 
  Not Sufficient

exc4libur · Answer

(1) sufic

b^2-8b+16=0, (b-4)^2=0, b=4

(2) insufic

b^2+16+8b-64=0, b^2+8b-48=0
(b+12)(b-4)=0, b={-12,4}

Ans (A)

monikakumar · Answer

What is the value of b?

(1) b(b - 8) = -16
(2) (b + 4)^2 = 64

1) b^2-8b+16 = 0
(b-4)(b-4) = 0
b=4
sufficient

2) b+4=8, b+4=-8
b=4, -12
insufficient

Ans A

What is the value of b? (1) b(b - 8) = -16 (2) (b + 4)^2 = 64

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Data Sufficiency (DS) Questions

What is the value of b? (1) b(b - 8) = -16 (2) (b + 4)^2 = 64

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards