How do I make calculations with percentages?
There is a simple way of making calculations with percentages.
Say you want to subtract from a numerical value x,20%. Then multiply it with 80/100.
Say you want to add 20%.Then multiply with 120/100.
Say you want to add 70%. Then multiply with 170/100.
In short,if you want to add x%,then multiply with (100+x)/100. If you want to subtract y% then multiply with (100-y)/100.Note that you can't subtract more than 100%.
Easy,right?
Now we will look on a particular tricky question. We have a TV that costs 1000 pounds.Then,the price of TV is reduced with 20%.After some time,the TV is increased with 20%. What is the final price of a TV?
Don't fall into the trap of saying that the final price is the same with the initial one,therefore 1000 punds.
1.) We reduce with 20% : 100080/100=800 pounds
2.) We increase the current price with 20%,so: 800120/100=960 pounds.
So the final price is 960 pounds.
Related Maths GCSE answers
All answers ▸Show that (x+2)(x+3)(x+4) can be written in the form of ax^3+bx^2+cx+d where a, b, c and d are positive integers.
Find an expression for the nth term of this sequence: 3 - 11 - 19 - 27 - 35 . The nth term of a different sequence is 2n^3 + 3. Write down the first 3 terms of this sequence.
By plotting appropriate graphs, find x to the nearest integer if x^2+3=2-4x.
f(x) = 3x - 2a || g(x) = 2ax + 1 || fg(x) = 2x + b/2