Because the number of days goes down as the number of children goes up, this problem type is inverse variation. We can solve this problem by the following steps:

20*6=24*x

120=24x

x=120/24

x=5

In this equation, x represents the total number of days that can be weathered by 24 students. This is down from the 6 days that 20 students could take shelter together. So the difference is 1 day less.

To solve for an inverse, we switch x and y and solve for y. Doing so yields:

1. Switch the  and  variables in the above equation.

2. Solve for :

If  varies inversely with , .

1. Using any of the two  combinations given, solve for :

Using :

2. Use your new equation  and solve when :

An inverse variation is a function in the form:  or , where  is not equal to 0. 

Substitute each  in .

Therefore, the constant of variation, , must equal 24. If  varies inversely as ,  must equal 24. Solve for .

Given a fractional algebraic equation with variables in the numerator and denominator of one side and the other side equal to zero, we rely on a simple concept.  Zero divided by anything equals zero. That means we can focus in on what values make the numerator (the top part of the fraction) zero, or in other words,

The expression  is a difference of squares that can be factored as 

Solving this for  gives either  or .  That means either of these values will make our numerator equal zero.  We might be tempted to conclude that both are valid answers.  However, our statement earlier that zero divided by anything is zero has one caveat. We can never divide by zero itself.  That means that any values that make our denominator zero must be rejected.  Therefore we must also look at the denominator.

The left side factors as follows

This means that if  is  or , we end up dividing by zero.  That means that  cannot be a valid solution, leaving  as the only valid answer.  Therefore only #3 is correct. 

The absolute value will always be positive or 0, therefore all values of z will create a true statement as long as . Thus all values except for 2 will work.

If we can find the sum of , , and 10, we can determine their average. There is not enough information to solve for  or  individually, but we can find their sum, . 

Write out the average formula for the original three quantities.  Remember, adding together and dividing by the number of quantities gives the average: 

Isolate : 

Write out the average formula for the new three quantities: 

Combine the integers in the numerator:

Replace  with 27:

To find the excluded values of a algebraic fraction you need to find when the denominator is zero. To find when the denominator is zero you need to factor it. This denominator factors into 

so this is zero when x=4,7 so our answer is 

When the denominator of a function is equal to 0, the function is undefined at that point. We can set x²-25 equal to 0 in order to find out what values of x make that true. 

We can factor to solve for x. 

 is an incorrect answer because for this value of x, the function equals zero, but it is not undefined.