Sequential Rate Problems Index

# Two Equation Rate Problems

Some rate problems require two equations. The solution of one equation determines a value needed for the solution of the second equation. The second equation produces the answer.
Problems in this class contain statements which have a fact in common. However, the common fact is not given and must be calculated. For example:
```        John missed 5 problems on his math quiz.  If there were 25 problems
total, what was his per cent correct?```
The problem asks for the percent correct, but the number of missed problems and the total number of problems is given. Therefore the formula
`        number correct + number wrong = total.`
must be solved for
`        number correct = total - number wrong.`
first. This formula is then used to calculate the number correct which is used in a second formula to calculate the percent correct.
`        (number correct / total) X 100 = percent correct.`
Example 3: Mary got 7 question wrong on a 35 question quiz. What was her percent correct on the quiz?
Example 4: John wants to purchase an item that costs \$35.00. If the sales tax rate is 6 percent, determine the sales tax and the total cost of the purchase.

The third type of Class I problems, sequential rate problems, requires a number of steps to achieve a solution.