1. Be familiar with the calculator you are using when playing CALC! Know how your calculator processes operations. If you need to use your calculator, you can use it more efficiently if you know how each key functions. Practice with large numbers. Estimate an answer before you press the = key.
2. Have pencil and paper available when you are playing CALC! A difficult multiplication involving a twodigit factor and a threedigit factor may require you to try many combinations before you hit on the correct one. Keeping track of these combinations by writing them down on paper will keep you from trying the same combinations and wasting time.
3. Knowing your basic arithmetic facts will enable you to see solutions to cards that can be computed mentally. Learn to "look before you leap." Quickly scan the card and the named digits and operations. If it is a oneoperation card, you may be able to use basic facts to do the card mentally.
4. If you have a twooperation card and three digits are to be used, what does that tell you? It means that the equation you are looking for involves three singledigit numbers. For example: suppose the named keys are 2, 6, 9, +, x to use for a target number of 24. Think: ___ x ___ + ___ = 24. The solution is 2 x 9 + 6 = 24. Of course, you know that 6 + 2 x 9 = 24, too. Similarly, if you have a twooperation card and four digits, then one of the numbers you are looking for has to be a twodigit number. If you develop the ability to do this kind of thinking before you start pressing calculator keys, you will win more cards using mental math.
5. The strategy of working backwards, especially with oneoperation cards, will help you win cards in playing CALC! For example, if you have to reach a target number of 2,162 using 2, 3, 4, 9 and x, you can work backwards by dividing 2,162 by different combinations of the digits 2, 3, 4, and 9. 2,162 divided by 23 = 94 so what will win the card is 23 x 94 = 2,162. With practice, you can even use the working backwards strategy with twooperation cards.
6. Here's another way of looking at the problem above. Look at the unit digit '2' of the target number, 2,162. Now look at the four digits you need to use: 2, 3, 4 and 9. The only two digits that will yield a product with a '2' in the unit's place are 3 and 4. So, you only have to check 93 x 24, or 94 x 23. Do this thinking with multiplication cards and you will save yourself lots of time and win more cards.
7. You may wonder why it was not necessary to check 923 x 4 or 924 x 3 in the above example. Both combinations have a '3' and a '4' in the units place. That's where your estimation skills come into play. The first combination, 900 x 4, which is 3,600, is greater than the target number, 2,192. Similarly, for the second combination, again using estimation, 900 x 3 is 2,700, which is also greater than 2,192. Using estimation, you don't even have to check 294 x 3 or 293 x 4. Using estimation skills is one of the best strategies to use in being successful in playing CALC!
8. You also want to look at patterns involving unit digits when you have a singleoperation addition or subtraction card. Suppose you have 1, 4, 7, 8, 9 and + to reach a target number of 560. Look at the unit digit of the target number. It's '0.' There's only one way of getting that '0' and that's with the '1' in the unit place of your one addend and the '9' in the unit place of the other addend. That and some quick estimation gives you: 481 + 79 = 560.
9. If you are using one of the decks with cards that show a square key, it is helpful to know the squares of the numbers from 1 to 25. 1 x 1 = 1, 2 x 2 = 4, 3 x 3 = 9, 4 x 4 = 16, etc. Write the squares of 1 to 25 on a 3 x 5 card. These squares should be memorized. Practice with a friend. Once you know these square numbers, some cards will now become "mental math" cards for you. Similarly, once you know these squares, you should be able to go in the other direction: square root of 144 = 12, square root of 196 = 14, square root of 529 = 23, etc. If a square root key is to be used; you can mentally juggle digits looking for square roots without using a calculator.
10. If you are using one of the decks with cards that show an exponent key, knowing the cubes of the numbers from 1 to 10 will also help you win cards. 1 x 1 x 1 = 1, 2 x 2 x 2 = 8, 3 x 3 x 3 = 27, 4 x 4 x 4 = 64, etc.
As you gain success at playing CALC! you may discover some great ideas for winning cards. Share them with other players by sending your good ideas to us at www.stokesco.com. Include your name, grade level, school, city, and state and we'll include it in this column and give you credit.

