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# MATHEMATICAL SHORTCUTS

Maths may not be your thing but it is hard to avoid in everyday life, however, help is at hand as there are many shortcuts around that can help make calculations a little easier.  Here are just a few ........

For some games with numbers click here

TIPS

To calculate the total of a bill including tax add 1 before multiplying.

Example 1        Price 150.95 plus tax of 0.065

Multiply 150.95 x 1.065 = 160.76

This also works in reverse -

160.76 divided by 1.065 = 150.95

Example 2        Price 150.95 plus 17.5% tax

Multiply 150.95 x 117.5% = 177.37

In reverse -

177.37 divided by 117.5% = 150.95

Thanks to KB for this one.

What this is actually doing is acknowledging the original figure is 100% and then adding on the additional percentage or (in this case) tax figure, giving a combined total as an answer.

Anything ending in an "even" number is divisible by 2.

Anything divisible by 9 is also divisible by 3.

Thanks to KB for these.

A quick way to do calculations is to drop the noughts at the ends of the numbers then replace them for your final answer.

Example   -  To add 120 + 90      add   12 + 9 = 21    then add back the 0  =  210

If you have to multiply a large number by 25, add two noughts to the number then divide by 4.  This is much easier to do, especially mentally.

Example:  167 x 25          16700        Divide by 4   =     4175

When faced with a little poser like 27.5% of 50 for example, I find it easier to call it 50% or 27.5.  It is easier to mentally divide 27.5 by 2.   It works every time.

Thanks for these Harvey Alexander

When multiplying numbers ending in 5 by themselves e.g. 75 x 75

Deal with the left hand numbers first

In this example the left-hand number is 7

Add 1 to this number i.e. 7 + 1 = 8

Multiply the original number 7 x the new number 8 = 56

Now deal with the right-hand numbers which are always 5 x 5 = 25

Therefore the answer is 5625

Here is another example -

35 x 35

3 + 1 = 4

4 x 3 = 12

5 x 5 = 25

Thanks to Allan Brown for this contribution

To make complex sums easier to handle, break down into simpler elements.

Example6 x 348

 first multiply 6 x 300 = 1800 then 6 x   40 =   240 then 6 x     8 =     48 Then add up all the elements:- 2088

A quick way to convert kilometres to miles is to drop the last digit and multiply by 6.

Example72 kilometres = 7 x 6 = 42 miles (approximately)

 10²   means 10 x 10 (known as 10 squared) =    100 10³   means 10 x 10 x 10 (known as 10 cubed) =  1,000 10 (with a little 4 - I couldn't find the symbol) means 10 x 10 x 10 x 10    (I think is known as 10 to the power of 4) 10 to the 4th power  -  Thanks Brenda = 10,000 10 (with a little 10) means 10x10x10x10x10x10x10x10x10x10 = 10,000,000,000 (1 followed by 10 noughts)