gurpreetsingh's approach to TEST VALUES was perfect for this DS question, but you can make it even easier. The prompt did NOT state that the 7 numbers had to be different/distinct/unique, so you CAN use duplicate numbers to save some time.
We're asked to find the MEDIAN of a group of 7 numbers. To do so, we need to arrange the numbers from least to greatest, then find the "4th" term.
Fact 1: 3 of the numbers are less than 10
Let's TEST VALUES:
IF the numbers are...
4 4 4 11 11 11 11
Then the median is 11
4 4 4 12 12 12 12
Then the median is 12
Fact 1 is INSUFFICIENT
Fact 2: 4 of the numbers are greater than 10
We can use the SAME TESTs that we used above...
Fact 2 is INSUFFICIENT
Combined, we can ALSO use the SAME TESTs from above.
GMAT assassins aren't born, they're made,