Fractions Basic skills: Cancelling, improper to mixed numbers, multiplying, dividing, adding, subtracting. Always change mixed numbers to improper fractions before doing calculations! Finding fractions of quantities - multiply by the top, divide by the bottom. Ratio - find the total number of parts before dividing. Decimals Basic skills: Adding, subtracting, multiplying, dividing. Changing Between Percentages To write an amount as a percentage: Finding a percentage of a quantity: Change the % to a decimal (divide by 100). Multiply by the original quantity. Increasing/decreasing a quantity by a percentage: Find new percentage after increase/decrease (100 - % increase/decrease). Change it to a decimal (divide by 100). Multiply by the original quantity. Compound interest: Add interest on to 100%. Change to a decimal (divide by 100). Multiply the original amount by this decimal for each year.