Solution: To save time and improve accuracy on DS questions in GMAT, learn and apply the Variable Approach.
Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.
Visit
https://www.mathrevolution.com/gmat/lesson for details.
Now we will solve this DS question using the Variable Approach.
Let’s apply the 3 steps suggested previously.
Follow the first step of the Variable Approach by modifying and rechecking the original condition and the question.
Let us assign the variable: men (m) ; women(w) ; children(c)
Given: m = 4k ; w = 7k ; c = 9k – where ‘k’ is a positive integer
We have to find the total number of people in the room => 5k + 3k + 7k = 20k – We have to find the value of ‘20k’
Follow the second and the third step: From the original condition, we have 4 variables (m, w, c, and k) and 3 equations (m = 4k; w = 7k; c = 9k). To match the number of variables with the number of equations, we need 1 more equation. Since conditions (1) and (2) will provide 1 equation each, D would most likely be the answer.
Recall 3- Principles and Choose D as the most likely answer. Let’s look at each condition separately.
Condition (1) tells us that the total number of men and women in the room is 11
=> 4k + 7k = 11
=> 11k = 11
=> k = 1
Therefore, 20k = 20 * 1 = 20
The answer is unique, so condition (1) alone is sufficient, according to CMT 2 - there must be only one answer
Condition (2) tells us that the number of children in the room is between 9 and 11
=> 8 < 9k < 10
=> 9k = 9
=> k = 1
Therefore, 20k = 20 * 1 = 20
The answer is unique, so condition (2) alone is sufficient, according to CMT 2 - there must be only one answer
** Tip 1: When condition (1) = condition (2) => 95% likely that answer is D
Each condition alone is sufficient.
Therefore, D is the correct answer.
Answer: D
