Forget the conventional way to solve DS questions.
We will solve this DS question using the variable approach.DS question with 3 variables and 1 equation: Let the original condition in a DS question contain 3 variables and 1 equation. Now, 3 variables and 1 equation would generally require 2 more equations to be able to solve for the variables.
We know that each condition would usually give us an equation, resulting in a total of 3 equations, one each from the original condition, condition (1), and condition (2). Since we need 2 more equations to match the numbers of variables and equations in the original condition, an equal number of equations and variables should logically give us an answer C.
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Let’s apply the 3 steps suggested previously. [Watch lessons on our website to master these 3 steps]
Step 1 of the Variable Approach: Modifying and rechecking the original condition and the question.=> We have to find the value of 'a' : Given a + b + c = 50
Second and the third step of Variable Approach: From the original condition, we have 3 variables (a, b and c) and 1 Equation ( a + b + c = 50). To match the number of variables with the number of equations, we need 2 more equations. Since conditions (1) and (2) will provide 1 equation each, C would most likely be the answer.Let’s take a look at both the condition together.Condition(1) tells us that c = 4a - 6 and Condition (2) tells us that the average of b and c is 2a.=> Average of b and c is 2a: b + c = 2 * 2a = 4a
=> b + 4a - 6 = 4a . Therefore , b = 6.
=> a + c = 44 and 4a - c = 6. Both equation will give us value of a.
Since the answer will be unique, both the conditions combined together are sufficient by CMT 2.The answer should be C.But this is a Common Mistake Type Concept4(A) in which if it easy to find C as an answer choose A or B as an answer. This is applied to key questions that involve integers, statistics, inequality. [watch our lessons to learn this tips]
Let's take each condition separatelyCondition(1) tells us that c = 4a - 6As there is no information about 'b', we cannot find the unique value of 'a'
[b]Since the answer is not unique, the condition is not sufficient by CMT 2.[/b]
Condition(2) tells us that b + c = 4a => a + b + c = 50
=> a + 4a = 50
=> a = 10
[b]Since the answer is unique, the condition is sufficient by CMT 2.[/b] Condition (2) alone is sufficient.So, B is the correct answer.Answer: B