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.

If each of the bowlers in a tournament bowled an equal number of games, what is the average (arithmetic mean) score of all the games bowled in the tournament?

(1) 70 percent of the bowlers had an average (arithmetic mean) score of 120, and the other 30 percent had an average score of 140.
(2) Each of the 350 bowlers in the tournament bowled 3 games.

From the original condition, we need to know the total number of bowlers (n) and the total score (s). In order to match the number of variables and the number of equations, we need 2 more equations. Since both 1) and 2) each has 1 equation, there is high chance C is the answer.

(Note: This is a statistics question, one of the key questions. Also, when the condition 1) has % and the condition 2) has a number, it is likely that the condition with % is going to be the answer.)

In a case of the condition 1), since the number of bowlers is n, from (0.7n*120+0.3n*140)/n, we get a unique answer and the condition is sufficient. Therefore, the answer is A. This is a type of question that appears within the score range of 50 and 51.

From con 1) and con 2), if one of the conditions is given by numbers and the other is given by ratio (percent,fraction), then the condition with ratio (percent,fraction) value has higher chance of being the answer.
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Bunuel. The question is very confusing. It says average score of all the games bowled. It doesn't specify that if it is asking the average score of bowlers or average score of a match in the tournament. I don't such language is actually used in actual GMAT. Actual GMAT questions are crystal clear.

To solve this question , I am considering that the average score of bowlers is being asked.

Given : each bowlers bowled equal no. of games in a tournament.
DS: average score of all games bowled in tournament.

Statement 1: 70 percent of the bowlers had an average (arithmetic mean) score of 120, and the other 30 percent had an average score of 140.
So average score of all bowlers = .7*120 + .3* 140 = 84 + 42 = 126
SUFFICIENT

Statement 2: Each of the 350 bowlers in the tournament bowled 3 games.
So, here we know the number of bowlers and the games but we don't know about the total score. So we can't calculate the average score of the bowler.
NOT SUFFICIENT

Answer A
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