# 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 = (1-3/4) N = 1/4 N

So, a fraction 1/4 of the number of students are present.

ok so its 1-3/4? 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/fra66m-multfract.html

http://www.themathpage.com/arith/multiply-fractions-divide-fractions.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!