Most pocket calculators have an "M" key, and most people do not know how to use it. Actually, this key, along with the associated memory keys, is easy to use and will help you do complex, multipart calculations. Computing something like the solution to binomial equations -- or even something more everyday, like A plus B times C minus D -- is a lot easier if you use the M key. With a little practice, you will be using pencil and paper only to write down your final results.
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Start using the "M" key instead of pencil and paper to keep track of partial results. For example, if the problem is to compute A plus B times C minus D, some people will start by calculating C minus D and writing it down. Then they will calculate A plus B and add it to the number that is written down. In a sense they are using the paper as "auxiliary memory." This is exactly what the M key does: it allows you to store partial results and use them in later stages of the calculation. Learning how to use the calculator's memory will save you the trouble of re-entering partial results into your calculator. That, in turn, will cut down the possibility of entry errors.
Learn what the basic keys do. They might be slightly different on your individual calculator, but there are three basic keys: one to clear the memory, one to put the current number on the screen into memory and one to one to display the current contents of memory to the calculator screen. The button that clears memory is typically labelled "CM," "MC," "C" or "Clear." This button sets the memory to zero. The memory-loading button stores the value on the screen to memory. It is typically labelled "M," or sometimes "M+" or "M-". If it is labelled "M+" or "M-" it will add, or subtract, respectively, the screen value to whatever is currently in your calculator's memory, so it is important that you clear the memory before beginning a calculation. The button that displays the memorised value to the screen is usually labelled "MR" or "RM." Experiment with your calculator to make sure you know which button does what.
Learn to use the "multiple memory" keys if your calculator has them. These keys allow you to use multiple memory locations. This feature is useful for calculations that would require you writing down several numbers on paper. For calculations like (A plus B) times (C minus D) divided by (E plus F), first do all the parts in parentheses, storing each in an individual memory location as you go. Then do the rest of the calculation with the stored numbers. The memory store keys will be named something like "Mn" or "Mn+" and the memory recall keys will be marked with something like "MRn" or "MRn+." When you use one of these buttons, a blank screen will appear where you can specify which memory location you are using.
Tips and warnings
- Always start a complex calculation from the innermost parentheses. This will make the storage of partial results natural. You will almost always have the values you need when you need them.
- It is easy to use the wrong partial results in your calculations, especially in unfamiliar complex calculations. The wrong partial results will produce the wrong ultimate results. Taking a few seconds to mentally map out what you are going to do -- before you start -- will usually take care of the problem.
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