When **math teachers ask** you to find the sum of a number, they are typically asking you to find the total value of all the components that make up that number.

For example, if your teacher asks you to find the sum of five numbers between 1 and 100, you *would add* up all the numbers to get the total number. The **total number would** be 105, since 1+2+3+4+5=10+5.

This is a very basic question, but it can be tricky when the numbers become very large or very small. Then, it becomes important to remember some of the more **fundamental math concepts** in order to answer it.

This article will discuss some tips for answering questions about sums in general, and how to answer questions about specific sums in particular.

## Example: x = 100.80

In this example, the unknown value is x, which is equal to 100.80. To find the total sum, we must find 100.80 as a percentage of something.

We can do this by first finding out how much 28% of 100.80 is, and then multiplying that number by 100.80. By doing this, we will get an approximation of how much the total sum is.

So let’s get started! First, we need to find out how much 28% of 100.80 is. To do this, take 100.80 and divide it by 0.28: you will get 339.95!

Now that we have found out how much 28% of 100.80 is, we can multiply that by 100.80 to get an approximation of the total sum: 339.**95 x 100** . 80 = $34 . 95 100.8!0!

This means that if the total sum was $100 . 80 , then the *actual total would* be $100 + ($34 . 95) = $104 . 85 !

The error in our approximation here is 0 . 85 , which is less than 5%.

## Method 1

The first method is to use the ratio rule. You can calculate the *unknown sum* by finding the ratio of what you do know and what you don’t know.

In this problem, you know the percent and you know the part of the whole that is $100.80, so you can use the ratio rule to find the *total amount*.

You start by dividing the part of the whole that is known by the percent that is known. This results in your first ratio.

Then, you divide one of those numbers by another number- in this case, 100.80 by $28.

You then put these **ratios together** to get your final ratio, which is 100.**80 ÷ 28** = 4:1.

## 28% of the sum = .28 * sum

The **next math trick** to learn is how to find the percentage of a number. How would you find what percent 28 is of a number?

You would have to find out how much 28 is and then divide that by the number. Then, you would have to subtract one from the other.

So, if 28 is $100 and 28 is 100-**80 cents**, then you would have to find out how **much 80 cents** is in dollars, which would be 80/100=80/100*100=8, and then -1 from 8, so 7. Thus, 28% of 100 is 7.

The reason this works is because you are first finding out what **percent 80 cents** is of 100 dollars, and then you are taking out the zeros and putting in ones to get how many it costs in cents.

## 0.28 * sum = 100.80

This equation gives you the sum of the percentage change, or how **much something changes** in proportion to *something else*.

It is useful when you have a percentage and you need to know what the **new number would** be after changing it by a certain amount.

For example, if you have a starting salary of $50,000 and receive a 3% raise, then your new salary is $50,000 + 0.03 * 50,000 = $50,500.00.

You can also use this equation to find the **starting number** if you know the percentage change. For example, if your new salary is $50,500 and the percent increase was 3%, then 0.03 * 50,000 = 100.80, which is the amount the salary increased by.

This equation can be rearranged to give you the sum if you know the percentage change and the original number.

## Divide both sides by 0.28

To find the sum of the difference between two numbers, you can divide both numbers by the difference. However, this only works if the difference is a small number (less than 5 or 6).

For example, if one number is 10 and the other is 12, then you can say that 12 is 2 higher than 10, or 10 is 2 less than 12. You can’t divide 10 by -2, so there’s no way to say that 12 is 10 higher than 10.

In this case, we need to use a different strategy. We’ll divide both numbers by the difference of 0.28 and see what happens!

If 28% of a sum is $100.80 then what is the sum? First, divide both sides by 0.28: S=S0.8 Then, switch S0.8 and SS, so that you have S8.. Now subtract S8.. (>. Now multiply both sides by 100.($100.($100.($100.(0.$100.$ So the answer is $100.$ What do you think? Does this make sense? Tell us in the comments! }} }} }} }} }} {{{{{{{{{{{{{ { { { { { { *{{{ {{{ {{{ {{({{({({(()())()))))))))))))))))) _____________________________________________________________________* If 28% of a Sum Is $100.80 What Is The Sum? – By JAYCEE TOLBERT on July 1st 2018 If 28% of a Sum Is $100.80 What Is The Sum? – By JAYCEE TOLBERT on July 1st 2018 If 28% of a Sum Is $100.80 What Is The Sum? – By JAYCEE TOLBERT on July 1st 2018 If 28% of a Sum Is $100.80 What Is The Sum? – By JAYCEE TOLBERT on July 1st 2018 If 28% of a Sum Is $100.80 What Is The Sum? – By JAYCEE TOLBERT on July 1st 2018If 28% of a SumIs$ 100 .

## Sum = 300.40

This question asks you to solve for the total amount of a group of values. In this case, the total amount is calculated by adding all of the *individual values together*.

You can see that there are six 0’s at the end of the 300.40, which means that this is a triple-*zero bill*. A triple-zero bill is a $100 bill, making the total amount $300.

Since there are twenty bills in a box and each one is worth $100, then the box value is also $3,000. The question asks how much money is in both boxes combined, so you would need to add up both values to get $6,000.

If you divided 6,000 by 20 (the number of boxes), then you would get $**300 per box**.

## Method 2

Another method is to write the number as a mixed number, then subtract the **smaller part** from the larger part. Then, add the **two parts together** to get the original number.

For example, we can write 28 as 25+3, then subtract 3 from 25 to get 22. We can then add 22 and *3 together* to get 25, the original number.

This is only possible if one of the parts is a **single digit**. If both numbers are two or more digits long, you cannot use this method.

Another example is writing 28 as 28+0, then subtracting 0 from 28 to get 28. You cannot write it as 28+0 and then add 0 to it to get 28, because 0 is not a real number.

## Suppose the original sum is S. |||||>

The first method is to use algebra: 28% of the sum equals a number which we will call ‘x’. We can write this as: 28%x=sum.

The given information tells us that 28%x=100.80 so we have: 1008(%)x=1008 and we can solve for ‘x’ by taking the percentage and dividing it out, giving us 25(%). So, if a number such as 25%, or 10%, or 50%, etc., is taken out of 100%, then that will be our answer.

The second method involves using an equation with two unknowns (S and X). We know that $300-$X=$100$. This means $X=$100-300-X=$300-X.$ We also know that $S$ must equal X plus $300$. This gives us two unknowns (X and S), but only one equation.

)

In this problem, the given information is the amount that must be taken out of the sum and the original sum. The difference between these two values is what we must solve for.

The ‘remove a number from a total’ problem can be generalized to any percentage, not just 28%. If 42% of a total is $100.80$, then 42% of the total must be taken out to equal $100.80$.

To solve for what percent of the total must be taken out to equal a given amount, first write an equation with two unknowns (S and X). We know that $X=$100-300-X=$300-X,$ and we know that $S$ must equal X plus $300.$ We also know that $X$ equals 100-300=-$200.

Then solve for X by taking it out of both sides and putting it on its own side.

Next, solve for S by taking it out of both sides and putting it on its own side.

Finally, take the percentage you got for X and divide it by 100 to get the percentage you need to take out of S.\u00a0

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