Follow any of the links below to be on your way to a better understanding of ratios, and good luck!
A fraction is also known as a ratio. For example, 3/4 is also the ratio of 3 to 4. Any statement (or equation) that says two ratios are equal is called a proportion. An important thing to remember when dealing with equal ratios is illustrated below.
3 15 4 * 15 - = -- Cross multiply. 4 20 3 * 20 4 * 15 = 3 * 20 60 = 60You can solve for unknowns in proportions by using that process.
4 21 1. Solve: - = -- m 5 Solution: Set the cross products equal. 4 * 5 = 21m Finish the problem by dividing both sides by 21. 20 -- = m 21Back to top.
If you are told there is a ratio of red marbles to blue marbles that equals 5:7 you are also told about two other ratios! You know there are 12 total marbles (5 + 7 = 12), so you know the ratio of red marbles to total marbles must be 5:12 and the ratio of blue marbles to total marbles must be 7:12. Also, it is usually helpful to write all these statements and then reread the problem to find any more information and to better understand the problem.
1. Problem: The ratio of red marbles to blue marbles is 5 to 7. If there are 156 marbles total, how many red marbles are there? Solution: Write down the information given and inferred. R = 5 B = 7 T = 12 With this information, there are three different proportions you can write. R 5 R 5 B 7 - = - - = -- - = -- B 7 T 12 T 12 The problem asks about red marbles and total marbles, so we will use the second proportion and replace the variable T with 156. R 5 --- = -- -> 12 * R = 5 * 156 -> R = 65 156 12Back to top.
Take the quiz on ratios. The quiz is very useful for either review or to see if you've really got the topic down.