Is 500 the average (arithmetic mean) score in the GMAT?

A. Half of the people who take the GMAT score above 500 and half of the people score below 500.

B. The highest GMAT score is 800 and the lowest score is 200.

Consider statement A alone and assume that half of the people scored 600 and half of the people scored 499, so average is not 500

Also there is a possibility that average can be 500 when half of the people score about 500 and the other half score below 500.

Hence we won't get unique answer using A.

Consider statement B alone: We can't find average just by knowing the highest and the lowest score.

Even by using both the statements, we cannot find the answer to the question. Option d) is the correct answer.