mathematics
posted by chrissy .
If 3/4 of a class is absent and 2/3 of those present leave the room, what fraction of the original class remains in the room?
my book says..
if 3/4 are absent, 1/4 are present
hows that so?
then it says if 2/3 of the 1/4 present , 1/3 of the 1/4 remain leave 1/3x1/4 =1/12 I don't understand? Do I add or?? Im not sure please help me
I think you'll find it easier if you introduce a variable for the number of students in the room. Suppose there are N students.
If a fraction of 3/4 is absent, then that means that the number of absent students is 3/4 N. Now the total number of students is N, so the difference
N  3/4 N is the number of students that are present.
N  3/4 N = (13/4) N = 1/4 N
So, a fraction 1/4 of the number of students are present.
ok so its 13/4? can you subtract that for me im not sure how to
Imagine a pizza that's cut into four equal parts. If your friends eat three pieces, they've eaten 3/4 of the pizza. That leaves 1/4 of the pizza for you.
Showing it mathematically:
1  3/4 =
4/4  3/4 = 1/4
Another way of looking at 1  3/4 is to think of money.
A dollar has 4 quarters (4/4). If you spend 3 quarters (3/4), you have one quarter (1/4) left.
The second part of your question states 1/3 of the 1/4 remain leave. Remember that the word "of" indicates you need to multiply. So ...
1/3 x 1/4 = ??
If you have trouble remembering how to multiply fractions, check one of these sites:
http://www.math.com/school/subject1/lessons/S1U4L4GL.html
http://aaamath.com/fra66mmultfract.html
http://www.themathpage.com/arith/multiplyfractionsdividefractions.htm
=)
Or does it state that 2/3 of the 1/4 present leave? If so, then the multiplication problem is 2/3 x 1/4 = ??
I wish they would of left me 2/4 of the pizza. Thank You very Much! that explains it!
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