Percentage

Hi,
Today we are going to talk about percentage.Percentage is a fraction of something out of 100.For example if you look at your grades on school grade book, 80% means, you have 80 points out of 100. Let us see how we can use this simple math fraction in science.We all can not survive with out water.We know that  75% of earth is water that means 75% of earths surface is covered with water.Water is made up of elements hydrogen and oxygen.The chemical formula of water is H2O. Let us see if we can calculate the percentage of oxygen in water.Water has a formula mass of 18.The atomic mass of hydrogen is 1 and the oxygen is 16.So for H2O,the mass will be 2x1+16=18.
     Let us see how we can calculate the percentage of oxygen in water.If we have 16 for every 18 of water then how much w e have in 100?
16/18 = A/100
16 x 100 = 18 x A 
Dividing both sides by 18 will give you 
A=(16 x 100)/18
The answer is 88.88%.
In this way you can calculate the percentage of any component in any compound or material.This simple math is used every day by people like engineers, chemists,etc...

subtracting integers

                 





Hi,
Today we are going to talk about subtracting integers.When you are subtracting integers you have to make sure you do it correct.you have to add both the negitive numbers and put a negitve sign in front.


lets do some exsamples.-3-12.First we do 3+12 and get 15.Because it is a negative we put a negive sign in front.It is very easy.