What is the interquartile range for 1,4,7,8,2,9,6,4,2

First, we need the numbers in order..
1,2,2,4,4,6,7,8,9

Q1 = 2
Q2 (middle number) = 4
Q3 = (7 + 8)/2 = 15/2 = 7.5

IQR (interquartile range) is Q3 - Q1 = 7.5 - 2 = 5.5 <==

30)
a)
We have to calculate the highest common factor (HCF) of 21 and 36.
21=3*7
36=2² * 3²
HCF (21,36)=3.
Therefore: the length of the side of the largest pieces into which Juanita and Samuel can cut the pizza must be 3 inches.
3 inches.

b)
Area (pizza)=21 in * 36 in=756 in²
Area (0ne piece of pizza)=3 in * 3 in=9 in².

number of pieces of pizza=Area pizza / area of one piece of pizza.
number of pieces of pizzas=756 in²/ 9 (in²/piece)=84 pieces.

answer=84 pieces. 

31)
x=number
-x=opposite of number "x"

The opposite of a number sometimes will be greater than the number itself.
if we have a negative number, the opposite of this number will be greater than the negative number.
Example:
x=-10
the opposite of -10 is 10
therefore: 10>-10

If we have a positive number, the opposite of this number will not be greater than the positive number.
Example:
x=10
the opposite of 10 is -10
Therefore: -10<10