There are two very simple methods on how to convert a decimal to a percentage:
rule of thumb: just always remember to move the decimal two to the right, and sticking a percent sign on the end. calculator: use the equation: p of (*) d = n (p: percent) Example: 40 is what percentage of 200?
40 = p * 200 p = 20%
Proportions: ratio = ratio
This technique comes in good handy when you need to double a recipe of any kind. Say a recipe that serves 8 people called for:
2 eggs
1/4 cup of milk
3 cups of flour
You need to double this recipe now; the equation you would make is: 2 eggs = x eggs x = 4 eggs
8 people 16 people
** you can continue this until your recipe is complete
To master division with decimals, you have to become very familiar with exponents and place values. The equation of a decimal being divided is the decimal being divided by the power of ten. Depending on the exponent is how many times you move the decimal place to the left to get your answer. Example: 5.06 divided by 10 ^ 4 = .000506
No matter if the exponent is negative of positive the decimal still moves to the left.
9's TRICK:
If any number is over 9, 99, 999, 9999, etc. that number will be repeated in the decimal form. It just depends on the place value of the 9.
1/9 = 0.11111111....
8/9 = 0.8888888...
* The pattern changes when the place value of 9 changes:
7/99 = 0.0707070707...
- the 0 represents the missing tens place value in the number 7
37/99 = 0.3737373737.....
- Notice how the 0 was replaced but a 3, because 37 has a number in the tens place.
* The pattern changes once again when the place value of 9 gets larger:
49/999 = 0.049049049049...
-Once again the 0 is representing how the number 49 does not have a number in the hundreds place
749/999 = 0.749749749749...
- The 0 was replaced with 7 because that us the number in the hundreds place.
***The reason why this numbers constantly repeat is because the number .999999 is actually equal to 1.
Converting Decimals to Fractions: Method #1: 0.27777....
= 0.2 + 0.7777... ( separate the lonely number from the repeating number)
= 2/10 + 0.777...
= 2/10 + 0.777... / 10
= 2/10 + 7/9 * 1/10 (just found out any repeating number is over a 9 number)
= 2/10 + 7/90
= 18/90 + 7/90 (common denominator multiply 2/10 by 9)
= 25/90
Method #2: 0.4191919... 10n = 4.191919... 100n = 41.91919... 1000n = 419.191919...
* you want to get two answers that have the same repeating decimal. (in this case 10n and 1000n do)
1000 = 419.191919... - 100 = 4.191919...
990 415
The answer then comes to 415/990
There is one very easy way of remembering the names for the certain placements in a decimal. Obviously the number before the decimal is the ones place, but to the right of the decimal is the tenths place. An easy way of looking at it is it's the same as the left of the decimal only your adding a "ths" at the end of each word.
tenths
hundredths
thousandths
ten thousandths
hundred thousandths
millionths
Also, the fraction form of the number is the number over the place value. Example: .005 is 5/1,000
.0006 is 6/10,000
There is also a expanded notation way of writing out a decimal. You just go down the list of numbers in order, concentrate on only one number at a time and then more on to the next one. Example: 34.8923 in expanded notation is --->
3(10) + 4(1) + 8(1/10) + 9(1/100) + 2(1/1,000) + 3(1/10,000)
Converting:
How do you convert a fraction into a decimal? Simple, just identify the place value of the denominator and move the decimal point that many times over. Example: 5/100 is .05
you want to put the number that's the numerator in the place value of the denominator. * I put the 5 in the hundredths place.
* practice converting fractions to decimals and decimal to fractions with this ACTIVITY
Vocabulary Terms:
rational numbers: any number that can be written in the form a/b where "b" isn't 0
