6.2.1 Adding and Subtracting Fractions with the Calculator
In the following exploration you’ll learn how to use the calculator to add and subtract fractions.
The calculator can be accessed on the left-hand side bar under the Toolkit.
Let’s try adding some fractions on the calculator.
Enter , then click , or press Enter on your keyboard. You should see the following:
So, adding one-fifth and two-fifths gives three-fifths, which should make sense.
Calculator Activity: Adding and Subtracting Fractions
Try the following additions and subtractions on the calculator.
Remember to clear the previous calculation before you start by clicking . Then, enter each calculation exactly as it is written. With complicated calculations like these, it is important to watch the top screen to make sure that the calculator is doing what you want it to do.
(a) Both fractions in this calculation are eighths, so you can add them directly, giving . Because the result is bigger than 1, it is given as a mixed number and then as a decimal number.
(b) You can subtract fractions, too. Both fractions are tenths, so subtracting
from gives , which reduces to by dividing both the numerator and the denominator by 2.
(c) This time the fractions have different denominators. The calculator has converted to twenty-fourths by multiplying top and bottom by 8.
The decimal form has been rounded here, so is not exact. For this reason, mathematicians often prefer to leave numbers as exact fractions rather than expressing them as rounded decimals.
(d) The calculator has converted all the fractions to twelfths, because twelve is the smallest number that 2, 3, and 4 all divide into evenly. The sum is written as . Now the fractions can be added, because they are all have the same denominator, giving the answer , or .
(e) This time, all the fractions are written as eighteenths, because 18 is the smallest number that 9, 3, and 2 divide evenly into. So, . The calculation in the numerator is . (You learned how to work with negative numbers in Unit 2.)
So, the answer is
Notice here that there is only room on the top screen for the calculator to display the first 8 decimal places of the decimal answer, but the answer correct to 14 decimal places is shown in the screen below.