Speed SAT Math Trainer

Speed SAT Math Tricks

There’s just no question about it – being able to perform quick mental arithmetic for any standardized test is an essential skill for speed and accuracy – especially the SAT Math section since it is primarily a logic test.

Below are listed all the tips, tricks, and shortcuts for dominating this speed math trainer. You should accept nothing less than consistently scoring nine stars for addition and multiplication on the “Basics” level if you truly wish to increase your score on the SAT Math.

Some of the following tips are taken from the book “Rapid Math Tricks and Tips” (c) 1992 by Edward H. Julius. The tips themselves are public domain and the author’s direct explanation or examples are not used. This is not the full list of tricks. Mistakes listed here do not reflect the author of the book.

Speed SAT Math Multiplication

To multiply by .4, 4,40,400 etc

Simply double the number twice and adjust the decimal, because 2×2=4

To multiply by .8, 8, 80, 800 etc

Double it three times and adjust the decimal, because 8 is 2 x 2 x 2

To multiply by .5, 5, 50, 500 etc

Divide by two and adjust decimals, because 5=10/2

When squaring two digit numbers that end in 5

Add 1 to the tens digit, multiply that number by the tens digit, then attach 25 to the end.

To square 65, as an example, add 1 to the 6 to get 7, 6*7 is 42, and attach 25: 65^2 = 4225

To multiply two digit numbers by .11, 11, 110, etc

Add the two digits your multiplying by 11 together and put their sum in the middle of the same two digits.

For Example: 12*11=?, 1+2=3,solution 132

*remember to adjust decimals for 1.1, .11, etc.

To multiply by .25,25,250, etc

Divide by four, and adjust the decimal. Because 2.5=10/4.

To divide by .25,25,250, etc

Multiply times 4 and adjust the decimal.

To multiply a one or two digit number by .99,99,990

Substract the number by one and call it value 1, then substract the number from 100 and call it value 2. Put the two values together.

For Example: To perform 87*99 quickly subtract 1 from 87 to get 86, and subtract 87 from 100 to get 13, 87*99=8613.

To multiply a two digit number times .101,101,1010

Write the number twice and adjust the decimal. 64*101=6464

To rapidly multiply by .125,1.25 12.5 etc

Divide by 8, adjust decimals. Because 5/4 or (10/8) is 1.25.

To rapidly divide by .125,1.25 12.5 etc

Multiply 8, adjust decimals. Because 5/4 or (10/8) is 1.25.

To multiply by .9, 90, 900 etc

Multiply the value you’re multiplying times nine, times 10 instead. Take that solution and substract the value you’re multiplying times nine from it. 9 x 28, we say 10 x 28 = 280 – 28 = 252.

To rapidly Multiply by .12, 1.2, 12, 120 etc

Multiply times 10 and call it value 1, multiply times 2 and call it value 2. Add the solutions.
12 * 60 = (10 + 2)*60 = (60*10) + (60*2) = 600 + 120 = 720.

To multiply by 15

Multiply by 10 and get value 1, divide by 2 then multiply by 10 and get value two.
For Example: 15*34 = (10+5)*34 = (10×34) + (5*34) = 370 + ((34/2)*10) = 510

Speed SAT Math Division

Note: Zero is divisible by every conceivable value except zero. Zero can be cut into two pieces, three pieces, four pieces, etc. evenly into any n pieces where n is the set of Natural Numbers.

Divisibility Rules:

A number is divisible by 2 if it is even

Example: 86, 942, 474, 50, and 66 are all divisible by 2

A number is divisible by 3 if the sum of all its digits is divisible by 3

Example: 861 8+6+1 = 15 1+5 = 6 So 861 is divisible by 3

A number is divisible by 4 if the last two digits are divisible by 4

Example: 924 24 is divisible by 4 so 924 is divisible by 4

A number is divisible by 5 if the last digit is a 0 or 5

Example: 95 and 620 are both divisible by 5

A number is divisible by 6 if it is divisible by both 2 and 3

Example: 774 7+7+4 = 18, and 774 is even so 774 is divisible by 6

A number is divisible by 7 if the result of subtracting twice the last number from the remainder of the number is divisible by 7 (Delete, Double, Subtract)

Example: 861 86-(2*1) = 84 8-(2*4)=0 So 861 is divisible by 7

A number is divisible by 8 if the last three digits are divisible by 8

Example: 1864 864 is divisible by 8 so 1864 is divisible by 8

A number is divisible by 9 if the sum of all its digits is divisible by 9

Example: 1854 1+8+5+4 = 18 So 1854 is divisible by 9

A number is divisible by 10 if the last digit is a 0

Example: 520 is divisible by 10

A number is divisible by 11 if the result of adding the digits in blocks of 2 from right to left is divisible by 11

Example: 32736 3 + 27 + 36 = 66 So 32736 is divisible by 11

A number is divisible by 12 if it is divisible by 3 and 4

Example: 288 2+8+8 = 18 and 88 is divisible by 4 so 288 is divisible by 12

A number is divisible by 13 if the result of subtracting 9 times the last digit from the remainder of the number is divisible by 13.

Example: 221 22-(9*1) = 13 So 221 is divisible by 13

A number is divisible by 14 if it is divisible by 2 and 7

Example: 252 25-(2*2) = 21, and 252 is even so 252 is divisible by 14

A number is divisible by 15 if it is divisible by 3 and 5

Example: 18510 1+8+5+1+0=15, and it ends in 0 so 18510 is divisible by 15

A number is divisible by 16 if it goes into the last four digits evenly

Example: 434864 4864 is divisible by 16 so 434864 is also

A number is divisible by 17 if the result of subtracting the original number from 5 times the last digit is divisible by 17

Example: 153 15-(5*3) = 0 So 153 is divisible by 17

A number is divisible by 18 if it is divisible by 2 and 9

Example: 9576 9+5+7+6=27, and it’s even so 9576 is divisible by 18

A number is divisible by 19 if the result of adding twice the last digit to the remainder of the number is divisible by 19.

Example: 133 13 + (2*3) = 19 So 133 is divisible by 19

A number is divisible by 20 if the last two digits are divisible by 20

Example: 940 40 is divisible by 20 so 940 is also