5 more Math tricks to Amaze your tutor

5 more Math tricks to Amaze your tutor Numeracy in the mind its not a talent, and not a gift. It is simply knowledge of some mathematical tricks. Now you will have additional knowledge that will help you use your mental abilities a bit more efficiently. Trick #1  Tip counting. If you need to leave a 15% tip, there is a simple way to do it. Calculate 10% (divide by 10), and then add the resulting number to its half and get the answer: 15%  ?f  $25 = (10% ?f 25) + ((10% ?f 25) / 2) $2.50 + $1.25 = $3.75 Trick #2 Division by 5. Actually dividing large numbers by 5 is very simple. All you need just multiply by 2 and move the decimal point: 195 / 5 Step 1: 195 * 2 = 390 Step 2: Move the decimal point: 39.0 or just 39. 2978 / 5 Step 1: 2978 * 2 = 5956 Step 2: 595,6 Trick #3  Subtraction  from 1000. To perform subtraction of 1000 you can use this simple rule: Subtract from 9 all the numbers except the last. And the last digit subtract from 10: 1000 -648 Step 1: subtract 6  from 9 = 3 Step 2: subtract 4  from 9 = 5 Step 3: subtract 8  from 10 = 2 352 Trick #4. Fast squaring, better method: a^2 = (a-b)(a+b)+b^2 So, e.g: 291 = (291-9)(291+9) + 9^2 = 282*300+81 = 84600+81 = 84681 With a little practice, you can do this in your head. Trick #5. Calculating 10 x, where x is a non-integer. The first thing is that x can always be broken down into x = k+y, where k is an integer and y is between 0 and 1. Then, obviously, 10k+y = 10k *10y. So the question becomes how do you do 10 y where y is between 0 and 1? Well, you can figure it out using some tricks when y = 0.1, 0.2, , 0.9, and then interpolate between those. For example, say you need to get 100.3. Then 210 = 1024 ~= 103.  So 210/10 ~= 103/10 = 100.3. So 100.3 ~= 2 (correct answer is 1.99). Then knowing 100.3 makes figuring out 100.6 and 100.9 easy. Also, 100.5 is easy, because 210 ~= 103, so 25 ~= 103/2 so 25 /10 = 3.2 ~= 100.5.