Suppose you spend $39.75 getting your hair done. Let’s calculate the sales tax. Assuming a tax rate of 6%, you enter the following into the Answers & Scratch window:
39.75*.06
Go ahead, try it! You can switch back and forth between this Help window and the live Answers & Scratch window by just clicking the mouse on the the desired window or selecting it from the “Windows” menu. After typing in the expression, press the “enter” key. Presto, your answer appears below your entry:
Answer= 2.385
However, dollars and cents figures are most appropriately expressed with only two digits after the decimal point. Therefore go to the “Solve” menu and select “Num. Format”. Type in “2” into the “Number of Digits” box and click on “OK”. Click on the Answers & Scratch window to select it again and click anywhere on the “39.75*.06” expression to select any part of it or deposit the insertion point in it. Press “enter” again. Real Answer™ copies the problem to the bottom of the window, and then places the answer under the problem line:
39.75*.06
Answer= 2.38
Suppose that while we were adjusting the number format, the sales tax rate went up to 7%. Fortunately, it’s very easy in Real Answer to calculate the results of an expression that is similar to one you have already entered. Select the “6” in any of the expressions you previously typed-in and replace it with “7”. Now just press “enter”. Real Answer automatically restores the line where you modified it to its original text, places a copy of the modified version at the bottom of the Answers & Scratch window, then calculates and displays the answer below that:
39.75*.07
Answer= 2.78
Neat and Handy! This Flex-Calc™ facility also enables the quick and easy calculation of the total price to pay including sales tax: Move the cursor to the expression “39.75*.07” and click and enter a “1” so that the expression becomes “39.75*1.07”. Then press “enter”. Real Answer™ appends:
39.75*1.07
Answer= 42.53
Let’s verify that result and in the process demonstrate other short-cuts. We will create a single line of text using two types of Paste commands. Hold down the “⌘” (the command key-- it has the propeller shape on it) and press the “e” key. (Or select “PastE PrEvious answEr” from the “Edit” menu.) Real Answer responds by typing the last answer’s numeric value into the window at the insertion point:
42.5325
(Real Answer always shows all the non-zero decimal places when it pastes the previous result (⌘E), even though we have selected the fixed number format with 2 decimal places for printing new results.) Type a minus sign and then copy “39.75” from a line above onto the end of the line you are building. (To copy something you can double click on it, select “Copy” from the “Edit” menu, click in the text where you want it to go, then select “Paste” from the “Edit” menu.) You should now have created this line:
42.5325-39.75
Then press “enter” to get the new answer:
Answer= 2.78
This is the original 7% sales tax we calculated. Remember that there are some digits hidden. The exact answer, 2.7825, would be displayed if you selected general format, or more digits to display. Real Answer rounded down the third and forth places after the decimal point. Sales clerks generally don’t; you would be likely to be charged $2.79 in a real-life situation. This illustrates an important point about Real Answer and all math tools: the answers they provide may have rounding errors in them. In fact, it’s always possible (although unlikely) that they may accidentally generate large errors. Therefore, for an important calculation, always check your results using some method that doesn’t rely on Real Answer.
