Main content

### Course: 4th grade > Unit 8

Lesson 3: Adding and subtracting fractions: word problems# Fraction word problem: piano

Sal solves a fraction word problem about practicing piano. The fractions have common denominators. .Created by Sal Khan.

## Want to join the conversation?

- At0:38, what is 3/4 of an hour, I kind of forgot.....(22 votes)
- Well a hour has 60 minutes right?

Thus 3/4 of 60 = 60*3 / 4 = 180/4 = 45 minutes!(31 votes)

- how much is 1/4 of an hour?(10 votes)
- 1/4 of an hour would be. 4/4 of an hour would be 60 minutes, so in order to get 1/4 you would need to divide 60 by 4. As a result, you would get 15 minutes.(11 votes)

- so 3/4 of an hour is 45 minutes right(13 votes)
- Yep! Exactly. Since 60/4=15, then multiply by 3 since it 3/4, so it would be 15*3=45, :)(6 votes)

- the answer is 2/4(8 votes)
- Yes... but remember to reduce your fraction. Fractions in answers should always be fully reduced.

2/4 = 1/2(9 votes)

- Hey! This video is not working what should I do

My internet is there I have completely 237 GBR left with me out of 500 gb

And I am using it(8 votes)- Go to the "help center" link at the bottom of the page and try looking in "troubleshooting"(9 votes)

- how can i represent my answer with picture numbers and words(6 votes)
- Basically, you can draw shapes that can be divided, then split it into the number of parts, then label the # of shapes and pieces. (Lastly, write the heading of your answer, such as: Mrs Ken's remaining cookies).

Try to keep the shapes as close to the topic as possible, it can help you guarantee a correct answer. For example, parts of cookies should be represented using circles.(6 votes)

- why so much videos and why not more math problems?(8 votes)
- Videos are for learning and problems are for practice. Also, there are enough problems. If you want more, buy a workbook or google some problems.(7 votes)

- How do I divide fractions, please help me ! urgently I'm struggling(6 votes)
- Is there something specific that you don't understand?(9 votes)

- how do you regroup fractions with mixed numbers.(9 votes)
- Why do we need to divide the answer if it is a fraction?(9 votes)

## Video transcript

Pedro is supposed
to practice piano for 3/4 of an hour every day. Today, he has practiced
for 1/4 of an hour. What fraction of an hour
does he need to practice? So let's visualize 3/4. So he needs to practice
3/4 of an hour. So if this represents
an entire hour, so let's divide it into fourths. So now, divide it into halves. Now, let's make it into
four equal sections. Now, it's into fourths. So he needs to practice
3/4 of an hour. That was my attempt
at drawing an arrow. So let me shade it in. So he needs to practice
3/4 of an hour. This gets us to 3/4
right over here. So he needs to practice 3 out
of the fourths of an hour. So this is 3/4. Now, it says he has already
practiced for 1/4 of an hour. So he's already
practiced for 1/4. So how much more does
he need to practice? Well, he needs to
practice this much more. And you might already
see the answer visually. But let's think about
how to represent it as a fraction expression. So let me write it like this. So this is how much
he needs to go. How much does he
need to practice? So he needs to do
a total of 3/4. He's already done 1/4. So if you subtract
1/4 from the 3/4, you're going to get this
amount right over here. You're going to get the amount
that he needs to practice. Now, this already has
the same denominator. So this is going to be
equal to 3 minus 1 over 4, which is equal to 2/4. And you see that
right over there. He still needs to practice 1
and 2 out of the fourths, 2/4. Now, 2/4, we know, is
the same thing as 1/2. There's a couple of
ways to think about it. You could say,
hey, look, this is half of the length
of this entire thing. It has a little bit on
this end and that end. Or if you make 4 equal
blocks, and if you were to shade in
2 of them, you see that you have shaded
in 1/2 of the blocks. This is the exact same
amount as if I just divide it into 2 sections and I
shaded in only 1 of them. 2/4 is the same thing as 1/2. And if you wanted to work
it out mathematically, you just have to
do the same thing to the numerator
and the denominator. So let's divide the
numerator and the denominator by 2, because they are
both divisible by 2. That's actually their
greatest common factor. So 2 divided by 2 is 1. 4 divided by 2 is 2. So what fraction of an hour
does he need to practice? He's got to practice
1/2 an hour.