Sherri's Helpful Hints

MATHEMATICAL HELP

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

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

Anything divisible by 9 is also divisible by 3.

If you have to multiply a large number by 25, add two zeros 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 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
Answer 1225

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

Example: 6 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 kilometers to miles is to drop the last digit and multiply by 6.
Example: 72 kilometres = 7 x 6 = 42 miles (approximately)