# How to Find 1 Minus the Number on the Screen of Almost Any Calculator

It has been about a week since I stopped to reflect on my study progress.  Since then, my focus has been once again on problem solving.  I have the SOA/CAS problems on paper, and the older SOA/CAS problems online at the Online Math Tests Home Page.  If you are studying for actuarial exams, you should use this resource.  Decide that you are going to solve 10, or 20, or however many problems each day, and soon many of the problems will start looking like old friends.

In the meanwhile, I had a sudden flash of insight this morning.  Part of doing exceptionally well on Exam P/1 is learning to use a simple calculator to its utmost efficiency.  I use the TI-30XA, which is the most simple of the simple.  I have really come to love this calculator, especially as compared to my big old clunky graphing calculator with a maze of counter intuitive steps leading to a given function.  The more that you can streamline a calculation, the less chance there is for errors.  For instance, most calculators have an inverse button (1/X).  without this inverse button, you need to either write down the number you would like to find the inverse of, then enter 1 divided by the number into your calculator, or you need to store the number in a memory on the calculator, then press 1, divided by, then recall the number from the memory.

Another very common calculation is the ones complement of a number.  In probability, we incessantly need to find the probability of an event not happening, which is simply 1- Probability (the event happening).  You might need to do this calculation several times in one problem.

So, up until this morning, here are the keypresses I used to find the complement.  Suppose that the number I need to find the complement of is on my screen.

1. {STO}
2. {1}
3. {1}
4. {-}
5. {RCL}
6. {1}
7. {=}

That is 7 keypresses, each one of which can be performed improperly.  My new method involves only 4 keypresses, using the ± button.

1. {±}
2. {+}
3. {1}
4. {=}

The added benefit is that I do not have to worry about intermediate values that I have stored in the memories (only 3 of them!) of the calculator.

To summarize:

# How To Find One Minus a Number on a Calculator:

1. Hit the ± button.
2. Add one to the result.