Converting from fraction to a decimal consists of dividing the denominator into the numerator. A fraction is a division. 2/5, for example, is the same as 2 divided by 5, so it can be expressed as the quotient. For example, 2/5=0.4. To express a fraction as a decimal, write the decimal as a fraction with a denominator that has a 1 followed by as many zeros as there are digits in the numerator. So 0.35 = 35/100.
Converting fractions to percents and vice versa is very easy because a percent is just a fraction over 100. So 35 percent is 35/100. To turn a fraction into a percent just convert the denominator to 100 and write the numerator with a percent sign. So 2/5 = 2/5 X 20/20 = 40/100 = 40 percent.
Multiplying is about the easiest thing you can do with fractions. The product of a/b and c/d is ac/bd. In other words, multiply the numerators to get the new numerator, and multiply the denominators to get the new denominator. So 2/3 X 4/5 = 8/15. To divide one fraction by another, invert the fraction that is the divisor, and then multiply. a/b divided by c/d is the same as a/b multiplied by d/c which is ad/bc. So 2/3 divided by 4/5 is 2/3 X 5/4 = 10/12 = 5/6.
Adding and subtracting fractions can be tricky -- especially when there are signs involved. The basic problem is that the denominators must be the same before adding or subtracting. When the denominators are the same, the numerator of the sum is the sum of the numerators and the denominator of the sum is the same as the denominators of the fractions being added. So 1/3 + 2/5 = 5/15 + 6/15 = 11/15.