This system can be solved a variety of ways, including graphing. To solve algebraically, write an equation for each of the different trains. We will use y to represent the distance from San Francisco, and x to represent the time since 8AM.

The blue train travels 80 miles per hour, so it adds 80 to the distance from San Francisco every hour. Algebraically, this can be written as .

The green train starts 380 miles away from San Francisco and subtracts distance every hour. This equation should be .

To figure out where these trains' paths will intersect, we can set both right sides equal to each other, since the left side of each is .

add  to both sides

divide both sides by 140

Since we wrote the equation meaning time for , this means that the trains will cross paths after 2.714 hours have gone by. To figure out what time it will be then, figure out how many minutes are in 0.714 hours by multiplying . So the trains intersect after 2 hours and about 43 minutes, so at 10:43AM.

To figure out how far from San Francisco they are, figure out how many miles the blue train could have gone in 2.714 hours. In other words, plug 2.714 back into the equation , giving you an answer of .

First, translate the problem into three equations. The statement, "Joule is three years older than twice Newton's age" is mathematically translated as

where  represents Joule's age and  is Newton's age.

The statement, "Newton is Toby's age younger than eleven years" is translated as

where  is Toby's age.

The third statement, "Toby is one year younger than Joule" is

.

So these are our three equations. To figure out the age of these dogs, first I will plug the third equation into the second equation. We get

Plug this equation into the first equation to get

Solve for . Add  to both sides

Divide both sides by 3

So Joules is 9 years old. Plug this value into the third equation to find Toby's age

Toby is 8 years old. Use this value to find Newton's age using the second equation

Now, we have the age of the following dogs:

Joule: 9 years

Newton: 3 years

Toby: 8 years

Divide the absolute values to get the magnitude of the answer.

Remember the following rules:

Positive divided by negative is negative.

Positive divided by positive is positive.

Negative divided by negative is positive.

Since we are dealing with two negatives, our answer will be positive.

This is a classic order of operations question, and if you are not careful, you can end up with the wrong answer!  

Remember, the order of operations says that you have to go in the following order of operations: Parentheses, Exponents, Multiplication, Division, Addition, Subtraction (also known as PEMDAS).  In this equation, you will start with the parentheses.  In the parentheses, we have 

.

But within the parentheses, you still need to follow PEMDAS.  First, we will solve the exponent, and the square of 2 is 4.  Then, we'll divide 16 by 4, which gives us 4, so we can rewrite our original equation as

.

We can now divide  into , which gives us

. 

The last step is to add and subtract the numbers above, paying careful attention to negative signs.  In the end, we end up with  because  added to  equals , and  minus  equals . 

For a number A to be divisible by another number B, A must share all of the prime factors of B.  For example, 100 is divisible by 10 because the prime factors of 10 (5 and 2) are found in the prime factors of 100 (2, 2, 5, and 5).  

In this problem, we have a number A that is divisible by 9 and 12.  First, find the prime factors of 9 and 12.  The factors of 9 are (3, 3).  The factors of 12 are (2,2,3).  So, to be divisible by 9 and 12, the number A must have the factors (2,2,3,3).  Multiply those together, and we get 2*2*3*3= 36.

So, A must be divisible by 36.  It could be divisible by the other answer choices, but since the question asked which choice must be right, we can only choose 36.

One way to do this:

Divide 100 by 6. The remainder will be the last digit.

Now divide the quotient by 6. This remainder will be the second-to-last digit.

The quotient is less than 6, so it is the first digit. The base-six equivalent of 100 is .

All of these choices are equivalent to the correct answer. But only  is in scientific notation.

Write the factors of the two numbers.

If a number is divisble by some number , then it is also divisible by all of its factors. Hence, if a number is divisible by , it is also divisible by , and . Thus, I and II are both true.

Rewrite the expression in fraction form.

Write out the common factors of both the numerator and denominator.

We can then see that the fraction can be reduced to  without having to conduct long division.

The answer is .