Data Sufficiency

On a recent trip, Mary drove 50 miles. What was the average speed at which she drove the 50 miles?
(1) She drove 30 miles at an average speed of
60 miles per hour and then drove the remaining 20 miles at an average speed of 50 miles
per hour.
(2) She drove a total of 54 minutes.

I chose A as I normally practice not having to go into depth with solving problems to save time. I thought statement 2 gave me information that wasn't needed. Can someone explain the answer?

Forget conventional ways of solving math questions. 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 independent equations ensures a solution.

On a recent trip, Mary drove 50 miles. What was the average speed at which she drove the 50 miles?
(1) She drove 30 miles at an average speed of
60 miles per hour and then drove the remaining 20 miles at an average speed of 50 miles
per hour.
(2) She drove a total of 54 minutes.

If we modify the original condition, vt=50(v:velocity, t:time taken), there are 2 variables (v,t) and one equations (yt=50) and 2 equations, giving a high chance (D) will be our answer.
Condition 1) t=54 (30min+24min)
Condition 2) t=54min
Each are sufficient, making the answer (D).

For cases where we need 1 more equation, such as original conditions with "1 variable", or "2 variables and 1 equation", or "3 variables and 2 equations", we have 1 equation each in both 1) and 2). Therefore, there is 59 % chance that D is the answer, while A or B has 38% chance and C or E has 3% chance. Since D is most likely to be the answer using 1) and 2) separately according to DS definition. Obviously there may be cases where the answer is A, B, C or E.

ill be taking my test on 12/12 i just heard of this method. I'm not sure if that is enough time to implement it into my practice/studying.

Max@Math Revolution wrote:Forget conventional ways of solving math questions. 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 independent equations ensures a solution.

On a recent trip, Mary drove 50 miles. What was the average speed at which she drove the 50 miles?
(1) She drove 30 miles at an average speed of
60 miles per hour and then drove the remaining 20 miles at an average speed of 50 miles
per hour.
(2) She drove a total of 54 minutes.

If we modify the original condition, vt=50(v:velocity, t:time taken), there are 2 variables (v,t) and one equations (yt=50) and 2 equations, giving a high chance (D) will be our answer.
Condition 1) t=54 (30min+24min)
Condition 2) t=54min
Each are sufficient, making the answer (D).

For cases where we need 1 more equation, such as original conditions with "1 variable", or "2 variables and 1 equation", or "3 variables and 2 equations", we have 1 equation each in both 1) and 2). Therefore, there is 59 % chance that D is the answer, while A or B has 38% chance and C or E has 3% chance. Since D is most likely to be the answer using 1) and 2) separately according to DS definition. Obviously there may be cases where the answer is A, B, C or E.