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29 Sep 2020, 01:43
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C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
5%
(low)
Question Stats:
92% (00:51) correct
8%
(01:10)
wrong
based on 74
sessions
History
Date
Time
Result
Not Attempted Yet
What is the value of ab?
(1) 3a+ 2b = 23
(2) a + 4b = 21
(1) 3a+ 2b = 23
(2) a + 4b = 21
Pure algebraic questions like this one are no longer part of the GMAT Data Sufficiency syllabus.
For relevant Data Sufficiency questions, please check the Data Sufficiency forum:
Data Sufficiency Forum
Data Sufficiency Forum
yashikaaggarwal
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29 Sep 2020, 12:52
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To find: What is the value of ab?
(1) 3a+ 2b = 23
one equation, two variance to solve.
Not possible.
(2) a + 4b = 21
one equation, two variance to solve.
Not possible.
Combining Both:
3a+ 2b = 23 ------------------(1)
(a + 4b = 21)*3 ---------------(2)
3a+12b = 63
3a + 2b = 23
---------------------- (using elimination)
10b =40
b =4
putting value of b in equation 2
a+4*4 = 21
a = 21-16
a = 5
value of AB = 5*4 = 20
(sufficient)
Answer is C
(1) 3a+ 2b = 23
one equation, two variance to solve.
Not possible.
(2) a + 4b = 21
one equation, two variance to solve.
Not possible.
Combining Both:
3a+ 2b = 23 ------------------(1)
(a + 4b = 21)*3 ---------------(2)
3a+12b = 63
3a + 2b = 23
---------------------- (using elimination)
10b =40
b =4
putting value of b in equation 2
a+4*4 = 21
a = 21-16
a = 5
value of AB = 5*4 = 20
(sufficient)
Answer is C
30 Sep 2020, 00:12
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Quote:
Step 1: Understanding statement 1 alone
(1) 3a+ 2b = 23
As there is no concrete value of and b, hence value of ab cannot be calculated.
When a = 1, b = 10, ab = 10
When a = 0, b = 23/2, ab = 0
Insufficient
Step 2: understanding statement 2 alone
(2) a + 4b = 21
As there is no concrete value of and b, hence value of ab cannot be calculated.
When a =1, b = 4, ab = 4
When a = 2, b = 19/4, ab = 19/2
Insufficient
Step 3: Combining statement 1 and 2
In linear equations, when ratio of coefficient of a is not equal to ratio of coefficient of b, there will be unique solution or one solution.
In these equations, ratio of coefficient of a= 3/1 is not equal to ratio of coefficient of b=4/2, hence there will be unique value of a and b.
Therefore, both the statements are required to calculate value of ab.
Sufficient
IMO C
