I mean for like retail purposes when you have to discount a percentage what is a fast way to work it out in your head?
The easiest ones.are where percent is divisible by 100. 25 for example, goes into 100 4 times. So to get 25% of 50, you divide 50 by 4, which is 12.50.
It's hard to explain without an example, but you have to find a simple way to break it down for non-divisible numbers. Like if you're trying to do 15% of $40 for example. Multiplying .15 by 40 might be sort of annoying to do in your head. But you know that 5% of 40 is 40 divided by 20 or .05 times 40. Which is 2, and a bit easier to do. 5% goes into 15% 3 times, so 2 times 3 is 6. so 6 is 15% of 40.
If it's like an annoying number like 17% or something. Round it to the nearest 5th percent. So it's be 15% instead.
It sort of comes with practice. Quick arithmatic is't something that comes instantly. After a while it'll be really easy.
Well, for example, if you would want to see 20% off a $30 pair of jeans, go through this:
That gives you 20% of $30. Then subtract that from your original amount:
$30-Y= Your new discounted price!
Besides that, here are some tips for improving mental calculating speed:
Whenever you deal with numbers that aren't easy to calculate in your head, like 16x47, then estimate and round them to the nearest easy number! So you get 15x50 instead, and if that's hard, make it even easier! Multiply 10x50= 500. Then multiply 5x50 which is 250. Add 500 to 250 and you get your estimated amount.
Hope this helps!
I would say start with an easy slices of the problem and work from there. Like if you have 300 dollar item, it's 17 percent off... start off with 10% off. That's minus 30 dollars.
From there you can go in all sorts of directions. You could say, if 10% is 30 dollars, then 30 divided by 10 is 3, which would be the amount for 1 percent. So you still have 7 more percent... 7 times 3 is 21. So the total amount off is 30 plus 21 = 51 dollars.
Or if you have a strange price like: $137.00 and it's 42 percent off... Divide the price by 100 (just move the decimal place two places to the left). That's $1.37 per percent. Then multiply by 42. I don't know how you'd do that in your head. Just keep a calculator nearby.
You could also practice Vedic Math.
THE KEY IS TO THINK IN 1, 10 AND 100 (The way metric measurement are meant to be used)
Let say 20% 0r 35% (or whatever , just replace the percentage i've used)
What is 20% OR 35% OF:
$1 = 20 CENTS / 35 CENTS RESPECTIVELY
$10 = $2 / $3.50 RESPECTIVELY
$100 = $20 / $35 RESPECTIVELY
SEE HOW SIMPLE IT IS WITH 1, 10, 100,OR EVEN 1,000 OR 10,000 (SAME PRINCIPLES APPLY)
BUT HOW YOU MAY ASK TO APPLY IT IN RETAIL SITUATION.
HERE IS HOW YOU DO IT.
LET SAY YOU BOUGHT A JEANS ON SALE FOR $89.95 WITH 15% DISCOUNT.
HERE'S THE STEP TO DO IT:
1. ROUND OFF TO THE NEAREST DOLLAR (IT BECAME $90)
2. NOW USE THE 10 FOR CALCULATION SINCE YOU ARE DEALING WITH TENS.(USE 10 FOR TENS, 1 FOR ONES AND 100 FOR HUNDREDS)
15% OF 10 IS $1.50
NOW SINCE YOU'VE GOT 9 TEN DOLLARS IN $90 YOU MULTIPLY
IT BY 9.
YOU CAN USE A 100 AS WELL BY WORKING BACKWARD
15% OF $100 IS $15
YOU KNOW THAT $90 IS $10 LESS THAN A $100 SO YOU DEDUCT 15% OF $10 WHICH IS $1.50
3. DEDUCT THE 15% DISCOUNT WHICH IS $13.50 FROM THE PRICE;
SO THE JEANS IS $77 AFTER 15% DISCOUNT
LET SAY YOU BOUGHT SOMETHING WORTH $27.WITH 12% DISCOUNT.
YOU WORK IT OUT LIKE THIS:
1. YOU WORK OUT THE TENS FIRST WHICH IS THE $20 OUT OF THE $27
12% OF $10 IS $1.20
2. WORK OUT THE ONES IN THIS CASE $7
12% OF $1 IS 12 CENTS
12 CENTS *7=84 CENTS OR 85 CENTS = $0.85
3. $2.40+$0.85=$3.25 (THIS IS THE 12% DISCOUNT)
4.$27-$3.25=$23.75 (THIS IS THE PRICE AFTER 12% DISCOUNT)
NOTE: When computing in your head especially if you are dealing with cents sometimes you have to accept approximation, something close enough is good enouign because you probably be only off by a few cents.
move the decimal and then subtract.
easy example: 10% of $100 = $1.00 then $100.00 - $1.00 is $99.00.