Just invert it like:

There you have your common denominator! Don't forget to multiply the numerator as well.
Answer:

Step-by-step explanation:
Given
The above table
Required
The standard deviation
First, calculate the class mid-point. This is the average of the class interval.
The mid-point x is:





So, we have:

Calculate mean




The standard deviation is:




The LCD is 6 on the left and 9 on the right.
The anwser is 4 becuase it is a rectangle and a rectangle has 4 sides
First calculate your percent as: 1-0.38=0.62. Then, multiply 0.62 by 50= 31. Your answer is 31