# Using the TI-108 Calculator

The TI-108 calculator is probably the most common calculator used in elementary schools. Therefore, future elementary school teachers should become familiar with their use. The TI-108 operates differently in some ways than most scientific calculators. It is of these differences that users that users should be aware.

When you first start using a TI-108, it is a good idea to hit the MRC button twice and then the ON/C button twice. This clears the memories of the calculator.

Perhaps the most important thing to realize is that a TI-108 does not recognize order of operations and it does not have parentheses. Recall that, given a string of operations, you first perform, from left to right, anything inside parentheses, then multiplication and division, then addition and subtraction. You can get around not having parentheses in some cases by using the M+ and M- buttons; these add or subtract the display to the value in memory. The MRC button recalls what is in the display.

Problem 1. If you enter 2 + 3 × 5 on a TI-108, what do you get? What do you get if you do this by hand? If you have access to a scientific calculator, what does that calculator give you?

Problem 2. Calculate the following numbers with the TI-108. For each one, write down the keystrokes you used. If you use the square root key, the calculator will take the square root of what is in the display, and then display the resulting square root.

1. 5 + 7.3 × 9,
2. (3 + 11) × 6 - 5,
3. (sqrt(5) - 1) / 2,
4. 16 × 4 + 7 × 12 - 11 × 14 + 43 × 9,
5. 1/2 + 1/3 + 1/4 + 1/5

If you perform one of the four arithmetic operations +, -, ×, or ÷, you need to hit the equal sign to get the answer. If you hit the equal sign a second time, the operation will be repeated. For example, entering 7 + 3 = will give you 10. Hitting the equal sign again will add 3 another time, giving you 13. Similarly, with subtraction and division, hitting the equal sign again gives you the same thing as hitting the operation and the second number again. However, multiplication is a little different. If you enter 3 × 2 = will give you 6. Hitting the equal sign again will give you 18 since it will multiply the display by 3. So, hitting the equal sign again is the same as hitting multiplication and the first number.

Problem 3. Perform the following operations by repeatedly hitting the equal sign. Write down the keystrokes you used.

1. 3 + 4 + 4 + 4,
2. 3 × 4 × 4 × 4,
3. 3 - 4 - 4 - 4,
4. 3 ÷ 4 ÷ 4 ÷ 4.

The percentage key can be used in the following two ways. First, if you want to add to a number a certain percentage of that number you enter the number, then plus, then the percentage number, then the percent key. For example, if you are calculating the final price, after the 6.25% sales tax, on a \$37 item, you enter 37, then plus, then 6.25, then the percent key. Once you hit the percent key you will have the final answer; you do not need to hit the equal key. Second, if you hit the minus key instead of the plus key, you will subtract the given percentage. For example, if a \$35 shirt is 20% off, the new price is obtained by hitting 35, then minus, then 20, then the percent key.

Problem 4. Compute the following prices.

1. \$143.26 plus 6.25% sales tax,
2. \$65.00 plus 15% tip,
3. \$45.99 after a 33% discount,
4. \$20.00 after a 25% discount and after 6.25% sales tax.