First of all take out the avg of the numbers in question. Which is 30. Average is sum of all the values divided by number of values.
There are 4 sets of options. Notice that 3 of those options have 5 numbers. Whenever there are five numbers to get the average of 30 the sum of those 5 numbers must be 150 because \(\frac{150}{5}\) = 30

Lets see the answer choices it is clearly obvious that option D has the same average as 30 because among the five values 1 value = 150 and rest =0 so there sum will be 150
Option C also adds to 150 so it also has the avg of 30
Option B adds to 145 so it has an avg slightly less than 30.
Option A has only 3 values so the sum should be 3*30 = 90 for the avg to be 30 which is the case hence it also qualifies
All options except option B have the same avg as the avg of numbers in question.

FYI: Option B can also be eliminated by weighing the difference between each number. Option B has 5 values. The median value is 30 i.e there are 2 values to the left of 30 and 2 values to the right of 30. Let us tally the left and the right part. Number '10' is 20 less than 30 similarly number '50' is 20 more than 30. There are two more numbers. number '20' is 10 less than 30. At this point we should look at the number to the right of 30 which is '35' and analyze if it is 10 more than 30 if it is then the avg is 30 however 35 is only 5 more than 30 hence we have a avg not equal to 30.

Try to use analysis when comparing values in statistics rather than doing calculation it will save time.