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Updated on: 31 Mar 2020, 02:24
Originally posted by GMATinsight on 31 Mar 2020, 01:23.
Last edited by GMATinsight on 31 Mar 2020, 02:24, edited 3 times in total.
Last edited by GMATinsight on 31 Mar 2020, 02:24, edited 3 times in total.
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D
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
65%
(hard)
Question Stats:
59% (02:17) correct
41%
(02:17)
wrong
based on 226
sessions
History
Date
Time
Result
Not Attempted Yet
If 2f(x) + 3f(-x) = 5x − 10, what is the value of f(-1)?
(A) -5
(B) -3
(C) 1
(D) 3
(E) 5
(A) -5
(B) -3
(C) 1
(D) 3
(E) 5
Source: https://www.GMATinsight.com
Updated on: 31 Mar 2020, 02:25
Originally posted by Archit3110 on 31 Mar 2020, 01:35.
Last edited by Archit3110 on 31 Mar 2020, 02:25, edited 2 times in total.
Last edited by Archit3110 on 31 Mar 2020, 02:25, edited 2 times in total.
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at f(1) ; 2f(-1)+3f(1) = -15---(a)
and at f(-1) ; 2(f1)+3f(-1)=-5---(b)
add a & b
we get
5f(1)+5f(-1) = -20
f(1)+f(-1) = -4
f(1)= -4-f(-1)
substitute value of f(1) in (a)
we get
2f(-1)-12-3f(-1)=-15
solve for f(-1) ; = + 3
Option D is correct
and at f(-1) ; 2(f1)+3f(-1)=-5---(b)
add a & b
we get
5f(1)+5f(-1) = -20
f(1)+f(-1) = -4
f(1)= -4-f(-1)
substitute value of f(1) in (a)
we get
2f(-1)-12-3f(-1)=-15
solve for f(-1) ; = + 3
Option D is correct
31 Mar 2020, 01:46
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This is very good question based on function:
2f(x) + 3f(-x) = 5x − 10
Putting x=1, 2f(1) + 3f(-1) = 5*1-10 = -5... eq(1)
Putting x=-1, 2f(-1) + 3f(1) = 5*(-1) − 10 = -15... eq(2)
Multiply equation 1 with 3 and equation 2 with 2 and subtract
5*f(-1) = -5*3- (-15*2) = 15
f(-1) = 15/5 = 3
Kindly check the Answer options
2f(x) + 3f(-x) = 5x − 10
Putting x=1, 2f(1) + 3f(-1) = 5*1-10 = -5... eq(1)
Putting x=-1, 2f(-1) + 3f(1) = 5*(-1) − 10 = -15... eq(2)
Multiply equation 1 with 3 and equation 2 with 2 and subtract
5*f(-1) = -5*3- (-15*2) = 15
f(-1) = 15/5 = 3
Kindly check the Answer options
GMATinsight
