Because 3 is greater than 1. I suppose it's possible to do it in your head, if you remember that in the world of fourths, 1 - 3 equals 2 but it's easier to subtract 3/4 from 17/4 or 3 and 5/4. As long as you can get to 3 and 1/2, it doesn't really matter, but don't tell your teacher I said that.
Anything minus itself equals zero.
In order to add or subtract fractions, the denominator (bottom number) has to be the same. In order to make it the same, you find the LCM and multiply the fraction by whatever is necessary to make the denominator the LCM. FOR EXAMPLE: 1/3 + 2/5 The LCM of 3 and 5 is 15. To make the 3 in 1/3 15, you multiply the whole fraction by 5 over 5 (it simplifies to 1 so you aren't really changing the fraction by multiplying it by 1). 1/3 * 5/5 is 5/15 You multiply 2/5 times 3 over 3 using the same principle 2/5 * 3/3 is 6/15 NOW you can add 5/15 and 6/15 to get 11/15.
The bottom number of a fraction is called the denominator. In order to add and subtract fractions with different denominators, it is necessary to make them the same, or "common." Example: 1/4 + 1/5. The common denominator is 20. 1/4 = 5/20 1/5 = 4/20 1/4 + 1/5 = 5/20 + 4/20 = 9/20
If 13 and 518 are both denominators, the LCD is 6734 If that's 1/3 and 5/18, the LCD is 18 and you can change 1/3 to 6/18
One "subtracts" or "subtracts from." I'm not sure how to "subtract by." Whatever.3/7 = 6/146/14 - 4/14 = 2/14 or 1/74/14 - 6/14 = -2/14 or -/1/7
Because you cannot subtract 3/4 from 1/4.
Probably not, but it depends on what you mean by "3th".
It means find the LCM of the denominators. In order to add and subtract fractions with unlike denominators, it is necessary to convert them to equivalent fractions with a common denominator. Example: 1/4 + 1/6 The LCM of 4 and 6 is 12. 1/4 = 3/12 1/6 = 2/12
1 1/2
It is not necessary. Sometimes, though, it is easier to find the probability of the complement and subtract that probability from 1.
1/3
If you can do it without, go ahead. But it helps to get the correct answer, since three is larger than one. If you re-name 4 and 1/4 to 3 and 5/4, it's easier to subtract 3/4 from it.
The answer is 143.75
-1/9
18
It is: 7/12
Yes. Anything minus itself is zero.