How to Do Math Problems in Your Head at Lightning Speed

You can solve math problems quickly in your head without a calculator by using a few tips.
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People who are amazingly fast at solving math problems in their heads might seem smarter than other people, but that's probably not true. Likely, they know a few mental math tricks. You can learn these simple tricks, which will help you in school and in the outside world -- because you won't always have a calculator by your side to rely on.

    Apply the rule of multiplying two-digit numbers by 10, which states that you can simply add a zero to the end of any number to quickly find the result of that number times 10 (for example: 10 x 12 = 120), to multiplying two-digit numbers by 11, for example, 32 x 11 = 352. Calculate the result in your head by adding the first and last numbers of the number to be multiplied by 11 together and putting that result in the middle. For example, 3_(3+2)2 = 352. If the middle number results in a two-digit number, add the first number to the beginning of the equation and leave the second number in the middle. For example, 88 x 11 = 8(8+8)_8 = (8+1)_6_8 = 968.

    Calculate the square of a two-digit number ending in 5 quickly in your head by multiplying the first digit by that digit plus 1 then adding 25 to the end of the number. For example, 45 x 45 = 4 x 5_25 = 2025.

    Calculate the result of any number times 5 with this simple trick. Take any number, divide it in half and consider the result. If the number is whole -- such as the number 4 -- meaning that the result has no decimal place followed by additional numbers -- such as 4.443 -- add 0 to the end of your result to get your answer. If the result is not a whole number but a number with a remainder, ignore the remainder and add 5 to the end of the result. For example, 2680 x 5 = 2680/2 and then add 5 or 0 -- in this case, 0 -- so the result is 13,400. Or, another example is: 5889 x 5 = 5889/2 and then 5 or 0 -- in this case 5. Drop the remainder and add 5 so that 2944.5 becomes 29,445.

    Quickly calculate a 15 percent tip on any amount by taking the total amount divided by 10 and adding half that number to the result. For example, 15 percent of $50 = (50/10)+ (50/10)/2 = $5 + $2.50 = $7.50.

    Use subdivision to quickly calculate large numbers in your head. For example, if you have to find the result of 32 x 125, divide the first number in half and multiply the second number by two until you have an easy problem to solve (16 x 250; 8 x 500; 4 x 1000 = 4,000).

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