CBEST Test Prep
CBEST Math Test Tips - Page three.
Mental Math Tips
Try 856 - 245,. Which of the following choices is a logical
choice for
the answer:
a. 600
b. 611
b. 625
c. 645
d. 590
You should have known it right off. 6 - 5 = 1, so it must end in a 1. The ONLY choice that ends in 1 is b. I don't need to do any math at all because I know it MUST be the correct answer.
The same thing must hold for multiplication and division.
How about a problem like 32 x 5 ? Split it up. We know it is larger that 30 x 5 or 150. We also know it ends in a zero because 5 x 2 = 10. But that's the answer! 150 + 10 = 160.
Suppose we 112 x 30. It must end in a zero. In fact, let's logically split it up. It is simply 100 x 30, plus 12 x 30, or 3000 + 360 or 3360. You should have already known it ends with a zero and is bigger than 3000.
Practice coming up with boundaries for the following problems:
12 x 52, 13 x 120, 400 x 25
Division is also done the same way. Think about what the answer is to 574 ÷ 14. Does it sound hard ? Perhaps we can change it to a multiplication problem. Think of 574 ÷ 14 as "what times 14 equals 574." What do you know so far? First of all, it ends in a 1 or 6 because those are the only numbers that will multiply by 4 to get a 4 on the end. We can try and get a boundary. 14 x 10 = 140, 14 x 20 = 280, 14 x 40 = 560 (If you did not know that, simply think that 14 x 40 is twice as much as 14 x 20). We need a little more than 560 to get 574. In fact, we know it ends in a 6 or 1. We can see it will be either 41 or 46. And logically, we can also see we need one more. The answer MUST be 41. So, if you don't like division, change it to a multiplication problem.
Try making up problems on your own and see how you can logically get the answer without doing arithmetic with pencil and paper. In no time, you will be a whiz at arithmetic and recognize that math is nothing to be "afraid" of or "avoided." You don't still only read picture books from kindergarten, do you? Why should you be content to do math on a basic level?
What about fractions? Percents? Decimals? Hey, numbers are numbers! They behave the same way no matter what game they are playing.
You need to know how decimals, fractions, and percents relate to each other, and how they are just numbers that will follow the above rules.
Know what is equivalent to 1/2.
Examples: 3/6 = 1/2, 2/4 = 1/2, 25/50 = 1/2, etc.
Know that 2 halves equals a whole no matter what form!
Examples: 2/4 + 4/8 = 1, 3/6 + 6/12 = 1, 10/20 + 50/100 = 1, etc.
Know how to make a "whole" from fractions.
Examples: 1/4 + 3/4 = 1, 2/5 + 3/5 = 1, 5/7 + 2/7 = 1, etc.
Know how to rapidly subtract fractions from a whole number.
Examples: 5 - 1/4 = 4 3/4, 6 - 5/7 = 5 2/7, 8 - 3/5 = 7 2/5, etc.
Know how to rapidly add a fraction to a whole number.
Examples: 5 + 1/4 = 5 1/4, 6 + 5/12 = 6 5/12, 10 + 5/6 = 10 5/6, etc.
Know how to tell what is more than 1/2 and what is less than
1/2.
3/4 is greater than 1/2, 5/6 is greater than 1/2, 7/12 is greater than
1/2, etc.
2/7 is less than 1/2, 5/11 is less than 1/2, 6/13 is less than 1/2,
etc.
Know that the larger the denominator, the smaller the
fraction. Know
this especially for those fractions that have a 1 on top.
Examples: 1/2 is more than 1/4, 1/12 is more than 1/13, 1/5 is more
than 1/10, etc.
Okay, so far everything has been easy, right? Well, if it was, then you know more about doing fractions than you thought you did. Let's try some problems.
[ Continue to CBEST Test Mental Math Page Four... ]
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