Max@Math Revolution wrote:In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem.

Remember equal number of variables and equations ensures a solution.

In original condition, 3c+5b+5i=195 then question is 7c+11b+9i=?
In this case, we have 3 variables (c,b,i) and 1 equation (3c+5b+5i=195)
We need 2 more equations. In this case, (1) is 1 equation, (2) is 1 equation so we have 2 equations. So C is the answer.

Why C? If you know our own innovative logics to find the answer, you don't need to solve the problem.

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The correct answer is not C but A.
The question stem does not require that we be able to solve for the 3 unknowns discussed in the problem.
Rather, the question stem asks only for the value of an EXPRESSION: 7c + 11b + 9i.
Given the information in Statement 1, we can determine the value of this expression.

If you look at the original condition, we get 3c+5b+5i=195, and the question becomes "7c+11b+9i=?"

In this case, we have 3 variables (c, b, i) and we have one equation 3c+5b+5i=195

In general, we have a solution whenever the number of variables match the number of equations, so we need 2 more equations right now to solve this problem.

In this DS question, condition 1 gives us one equation, and condition 2 gives us another equation.
Taking the two conditions together will give us the two more equations we need, so the answer is C.

Max@Math Revolution wrote:If you look at the original condition, we get 3c+5b+5i=195, and the question becomes "7c+11b+9i=?"

In this case, we have 3 variables (c, b, i) and we have one equation 3c+5b+5i=195

In general, we have a solution whenever the number of variables match the number of equations, so we need 2 more equations right now to solve this problem.

This line of reasoning does not apply to the posted problem.
The question stem does NOT ask us to solve for the 3 variables.
It asks only for the value of 7c + 11b + 9i.

From my post above:

Given equation: 3c + 5b + 5i = 195.
Question: What is the value of 7c + 11b + 9i?

Statement 1: 5c + 7b + 3i = 217

Try to combine this equation with the given equation so that the coefficient in front of c is a multiple of 7.

Multiplied by 3, the given equation 3c + 5b + 5i = 195 becomes 9c + 15b + 15i = 585.
Stacking this equation with the equation in statement 1, we get:

9c + 15b + 15i = 585
5c + 7b + 3i = 217

Adding the two equations, we get:
14c + 22b + 18i = 802.

Dividing the equation above by 2, we get:
7c + 11b + 9i = 401.
SUFFICIENT

As you can see, Statement 1 provides sufficient information to determine that 7b + 11b + 9i = 401.
The correct answer is not C but A.

In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem.
Remember equal number of variables and equations ensures a solution.


In original condition, 3c+5b+5i=195 then question is 7c+11b+9i=?

In this case, we have 3 variables (c,b,i) and 1 equation (3c+5b+5i=195)

We need 2 more equations. In this case, (1) is 1 equation, (2) is 1 equation so we have 2 equations. So C is the answer.



If you know our own innovative logics to find the answer, you don't need to actually solve the problem.

www.mathrevolution.com

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Max@Math Revolution wrote:In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem.
Remember equal number of variables and equations ensures a solution.


In original condition, 3c+5b+5i=195 then question is 7c+11b+9i=?

In this case, we have 3 variables (c,b,i) and 1 equation (3c+5b+5i=195)

We need 2 more equations. In this case, (1) is 1 equation, (2) is 1 equation so we have 2 equations. So C is the answer.



If you know our own innovative logics to find the answer, you don't need to actually solve the problem.

www.mathrevolution.com

- The one-and-only World's First Variable Approach for DS and IVY Approach for PS that allow anyone to easily solve GMAT math questions.

- The easy-to-use solutions. Math skills are totally irrelevant. Forget conventional ways of solving math questions.

- The most effective time management for GMAT math to date allowing you to solve 37 questions with 10 minutes to spare

- Hitting a score of 45 is very easy and points and 49-51 is also doable.

- Unlimited Access to over 120 free video lessons at https://www.mathrevolution.com/gmat/lesson

- Our advertising video at https://www.youtube.com/watch?v=R_Fki3_2vO8

This question is already solved with only Statement 1.

so Answer is A

Max@Math Revolution wrote:
In original condition, 3c+5b+5i=195 then question is 7c+11b+9i=?

In this case, we have 3 variables (c,b,i) and 1 equation (3c+5b+5i=195)

We need 2 more equations. In this case, (1) is 1 equation, (2) is 1 equation so we have 2 equations. So C is the answer.

You aren't being asked to solve for all three variables independently, though.

Given the two equations (3x + 5y + 5z) = 195 and (5x + 7y + 3z) = 217, we can subtract the first from the second, then divide the result by 2, which gives (x + y - z) = 11.

We then simply compute (3x + 5y + 5z) + (5x + 7y + 3z) - (x + y - z), which simplifies to 7x + 11y + 9z, which is what we wanted.

So the answer is clearly not C.