If (3 + a)(a/10 - 0.4) = -1, then a could be

Question

If  (3 + a)(\frac{a}{10} - 0.4) = -1 , then a could be

A. -4
B. -2
C. 1
D. 2
E. 4

BrentGMATPrepNow · Accepted Answer

Another approach is to eliminate the fractions/decimals first.

Given: (3 + a)(a/10 - 0.4) = -1
Multiply both sides by  10  to get: (3 + a)(a/10 - 0.4)( 10 ) = (-1)( 10 )
Simplify: (3 + a)(a - 4) = -10
Expand and simplify: a² - a - 12 = -10
Add 10 to both sides: a² - a - 2 = 0
Factor: (a + 1)(a - 2) = 0

So, EITHER a = -1 OR a = 2

Answer: D

Nikkb · Answer

given (3+a)(a/10−0.4)=−1

=>(3+a)(a−4)=−10 = (-10*1)=(-2*5)

if we try to get (-10*1) => a=7 => 10* 3 ... a=5 => 8*1

try to get (-2*5) => a=2 =>(5)*(-2) answer

Answer: D

BrentGMATPrepNow · Answer

Alternatively, once you get to the point where you have the equation (3 + a)(a - 4) = -10    , you could easily plug in the answer choices until you found the one that satisfies the equation (3 + a)(a - 4) = -10

Cheers,
Brent

sashiim20 · Answer

(3 + a)(\frac{a}{10} - 0.4) = -1

(3 + a)(\frac{a- 4}{10}) = -1

(3 + a)(a- 4) = -10

3a -12 + a^2 - 4a = -10

a^2 - 4a + 3a -12 +10 = 0

a^2 - a -2 = 0

(a -2)(a+1) = 0

a = 2  or  -1

Therefore " a " could be  2

Answer (D)...

chetan2u · Answer

Hi...

if I want to do it fast and use logic..
 \frac{a}{10}-0.4=\frac{a-4}{10} 
so looking at the choices, 3+a should be a factor of 10...
A) so a could be -4 as  3-4=-1  but then the RHS will become positive so discard
B) a as -2 would make 3+a as 1 but  \frac{a-4}{10}  can never be -1
C) a as 1 gives 3+a as  3+1=4 .. not a factor of 10.. Discard
D) a as 2 gives 3+a as  3+2 = 5 , a factor of 10.. try substituting .. FITs in
E) a as 4 gives  3+4=7 ... Discard

substitution this way would be way faster than finding solution of a

YouHamia · Answer

Simplifying the equation we get:
(3+a)(a/10-0.4)=-1
(3+a)(a-4)(1/10)=-1
(3+a)(a-4)=-10

Replacing a accoding to the choices:
A. -4 => (3-4)(-4-4) = -1*-8 =8 (Discard)
(...)
D. 2 => (3+2)(2-4) = 5*-2 = -10 (correct)

ScottTargetTestPrep · Answer

We can simplify the given equation:

(3 + a)(a/10 - 4/10) = -1

(3 + a)  = -1

(3 + a)(a - 4) = -10

a^2 - a - 12 = -10

a^2 - a - 2 = 0

(a - 2)(a + 1) = 0

a = 2 or a = -1

Answer: D

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If (3 + a)(a/10 - 0.4) = -1, then a could be

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If (3 + a)(a/10 - 0.4) = -1, then a could be

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