14. the mode of the data set is 21. what number is missing?

21, 17, _, 25, 23, 13

19. the mean of the data set is 18. what number is missing?

21, 11, _, 27, 22, 13, 16

20. the median of the data set is 81. what number is missing?

82, 87, _, 77, 70, 80, 88

The answer for the first one would be 27.
The answer for the second one would be 16.
The answer for the third one would be 83.

14. The mode is the number in a data set that happens most frequently. Since we have a 21 and the mode is 21 then the missing number has to be 21.

19. The mean is the average of all the data in the set. That means...

(X+21+11+27+22+13+16)÷7= 18

X + 110/7 = 18
X + 110 = 126
X = 16

The missing number is 16

20. The median is the central number in a data set. Put the numbers in order...

70, 77, 80, __, 82, 87, 88

It tells us that 81 is the median, so that has to be the missing number because it fits as the central number (the middle number in the data set). There are 3 numbers before it and after it.

Missing number is 81