What is an easy way to calculate sales discounts in your head?

Question

I know 10% you just drop the last number and subtract it, so 10.99 you drop the last nine so it is 1.09, round up to 1.10 discount...... But what about 15%? 20%? How can you calculate those in your head?

Answer 1

Take half of 10 percent and add it to the ten percent number for 15. Double what 10 percent comes out to for 20 percent. I usually try to use an anchor number that is close to the original. So if it's 63 percent; just take the ten percent, multiply that by 6 for 60 and add three 1 percents. Sounds more complicated when I explain it I think, but it is conceptually easy.

Answer 2

Three almost instantaneous steps:
1) Feel
2) Subtract (as I usually want to no the discounted price, and not the amount being discounted.)
3) Ignore details and multiply (provided u have memorize the time-table for 2-9).
Steps 2 and 3 might interchange, especially when discount is > 50%.

E.g. 10.99 @ 10% discount
1) Feel that the price is < 11
2) 10% discount: i.e. cost 90%
3) 9* 11 = 99, thus it is 9.9

E.g. 10.99 @ 20% discount
1) Feel that the price is < 11
2) 20% discount: i.e. cost 80%
3) 8* 11 = 88, thus it is 8.8

E.g. 10.99 @ 15% discount
1) Feel that the price is < 11, and 15 * 2 = 30
3) 30% discount: i.e. 3 * 11 = 33, so 15% relate to 165
2) 11-1.65 ~ 9.5

By the way, the way you described is NOT calculation, but figure manipulations. That's why you need to ask about other than 10% discount. Also, if you do found different ways for the different discount percentages, you will have many things to remember in your head. I strongly discourage these non-mathematical methods to "calculate."

Answer 3

Since most sales are 10, 15, 20, 25, or 30%, build on the 10% idea.

Just take 10% and multiply it by appropriate amount. (So, if the sale is for 30% off, that's more or less 3 x 10%. So, take10% of $10, which is $1, and multiply it by 3. That is $3, so you get a $3 SAVINGS.)

If it is a something-5%, like 25%, just figure the 20% amount, and then add half of a 10% (because, again, 5% is half of 10%). So, for ex., if it's 25% off of a $10 item, 10%=$1, and 20%= $2. Half of the 10%= 50 cents. Add the $2 and the 50 cents to get the $2.50 SAVINGS. You get the idea.

Now, here's a little trick I use if you get above 40% (50% is easy, just divide the regular price by half). Most things don't go over 35% off unless they are on clearance, and then they usually follow the 50%, 75%, etc. At that point, you have a better chance figuring out what you are PAYING right off the bat.

For ex., at 75% off, you are PAYING 25% of the full price. Just figure out what the 25% is (10% amount x 2 plus 5%) and you have your final price.

It may sound complicated at first, but it's really not. Practice it and you'll get good at it in no time! (I can't do math in my head to save my life, but I can do this!)

Answer 4

are you kidding.. thats like 4th grade stuff...
20% is 10 twice... 15 is 10 adding half more

Answer 5

Just give the cashier a twenty and hope the computer's got it right...

Answer 6

easiest way ever:

put out the cellular and punch in the numbers;D

Answer 7

You take third grade math over again.

Answer 8

i can't tell you, it's in my head