How to Solve Basic Math Sums

While rote memorization will help you to learn your addition, subtraction, multiplication and division tables, slightly more advanced skills are necessary to solve basic math sums involving fractions or percentages. Being able to solve these basic math sums comes in handy in many unexpected ways through a typical day, especially when shopping for groceries or calculating the tip or gratuity for a restaurant bill.

Instructions

Finding Percentages

1. Write the number you're supposed to find the percentage of as a decimal. If there's a decimal point in the number already--for example 87.2 already has a decimal point--you're done. If you're faced with a number such as 27 that has no decimal, just add the decimal after the last digit. That would make 427 look like "427."

2. Move the decimal point two places to the left. So for example 427. will look like 4.27 once you've moved the decimal point. The number you're left with after moving the decimal point--in our example, 4.27--represents 1 percent of the original number.

3. Multiply the number you arrived at--one percent of the original--by however many percentage points you were tasked to find. So for example if you had been tasked with finding out what 12 percent of 427 is, you would multiply 1 percent of 427 (4.27) by 12 and arrive at the final answer of 51.24.

Multiplying Fractions

1. Write all the fractions side by side on the same line, with a dot between each fraction to indicate multiplication. For example, if you're multiplying 3/4 by 2/5, you'd write 3/4 (dot) 2/5.

2. Multiply all the numbers on the tops of the fractions together. Write the total off to the side. Following the example, that would be 3 x 2 = 6, so you'd write 6 off to the side.

3. Revisit the numbers on the bottoms of the fractions and multiply all of them together, too. In the case of our example that would by 4 times 5 which works out to 20. Write this new total underneath your previous total and draw a horizontal line between them. You've just multiplied the fractions--the new fraction you just wrote is the product of all the other fractions. To conclude with the example, the answer for 3/4 x 2/5 = 6/20.

Dividing Fractions

1. Write the two fractions to be divided side by side. If you're trying to divide 5/8 by 1/8--also known as dividing 1/8 into 5/8--you'd write 5/8 first, then 1/8 afterward.

2. Scratch out the divisor--the second of the two fractions, the one that is being divided into the other fraction--and rewrite it upside down. In other words write the numerator on the bottom instead of the top of the fraction, then put the denominator, which used to be the number on the bottom, on top of the new fraction. For example, this would mean writing 1/8 as 8/1.

3. Multiply straight across the top of the new fraction pair and write down the total off to the side. In the example, that would be 5 (from the first fraction) x 8 (from the upside down fraction) = 40. Multiply across the bottom and write that total underneath the previous total; draw a horizontal line between them. In the example, the new denominator would be 8 x 1 = 8. The two totals together represent the answer to your division problem, represented as another fraction. The answer to the example is 40/8. Note that you can do this division with whole numbers; 40 / 8 = 5, so the actual answer can also be written simply as 5.

Adding and Subtracting Fractions

1. Write the two fractions to be added or subtracted down next to each other.

2. Multiply across the bottom of the fractions and write the answer off to the side as the bottom of a new fraction. So for example if you're subtracting 5/9 from 7/8, you would first write 7/8 - 5/9, then 8 x 9 across the bottom and off to the side write 72 as the denominator or bottom of a new fraction.

3. Multiply the top number of the fraction on the left by the bottom number of the fraction on the right. In our example, this would mean multiplying 7 x 9 = 63. Write this on top of the new denominator.

4. Go back and multiply the top number of the fraction on the right by the bottom number of the fraction on the left. Write this new product on the right of the previous product. So to continue with the example, 5 x 8 = 40, and then writing 40 just to the right of 63.

5. Place the operation sign you're dealing with in between the last two numbers you wrote. In this case we were asked to subtract one fraction from the other, so we'll put a minus sign between the numbers. We now have a fraction with 63 - 40 on top and 72 on the bottom.

6. Perform the operation indicated on top of the fraction. In this case that means subtracting 40 from 63, which yields a total of 23. Write this new number off to the side on top of the denominator you arrived at, which in our example is 72. This is the final answer.

References

• MathPower.com Student Tutorials