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## 4th grade

### Course: 4th grade > Unit 8

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

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

## Want to join the conversation?

- what if the two top numbers are bigger than the bottom number like this: 2/8+7/8=9/8(10 votes)
- I think you need to multiply the two denominators that aren't the same and find the LCM(5 votes)

- Where do you get the spider problem when its not in in the practice?(10 votes)
- It's just an example. Not all video problems are the same as practice problems.(5 votes)

- what are spider eyes in math(9 votes)
- its just a demonstration.(1 vote)

- So, fractions do not only represent equal parts of a whole, but are groups or things?(5 votes)
- True. If a class has 30 students and 28 are present at morning assembly then 28/30 are present. The whole in this case is all the students of the class combined. (This can be simplified to 14/15 though in a real case scenario it probably wouldn't be).

You can make such a set out of whatever you feel like: books you've read out of all the books you own. Capitals you've visited out of all the capitals in the world etc.(8 votes)

- Why spiders khan academy?? Why not deserts?(8 votes)
- why does the mid spider look cute

upvote if agree downvote if disagree(8 votes) - it makes sents

and its making me sherver(5 votes) - does this mean that spider can see with 360degree??(7 votes)
- The pictures made me uncomfortable(7 votes)
- Is it just me or does the first spider have 6 eyes?(7 votes)
- the other two are hidden(2 votes)

## Video transcript

A common house
spider has 8 eyes. If a spider is looking at
you with its 2 front eyes and 3 of its other eyes,
what fraction of its eyes are looking at you? And just to show that we're
not making this stuff up, this is actually
pictures of spiders. And you see in every
one of these pictures they have eight eyes, even
this one's got other eyes right over here-- 1,
2, 3, 4, 5, 6, 7, 8. I never even realized this. This is actually quite creepy. But anyway, let's actually
focus on the problem. So it's looking at you
with 2 of its 8 eyes. So the 2 front eyes represent
what fraction of the eyes? Well, it represents
2 of the 8 eyes. You could look at
it right over here. You have 8 eyes. We have the 2 front eyes. That's 1 and 2 of the 8. And it says it's also looking
at us with 3 of its other eyes. So it's also looking at
us with 3 of the 8 eyes. And so you can
imagine that might be that one, that
one, and that one. So this is really
about adding fractions. This is about adding 2/8 of
something to 3/8 of something. So what fraction of its
eyes are looking at us? Well, it's still going
to be a fraction of 8. It's going to be still out
of 8-- 2 plus 3 over 8, which is just going to be
equal to 5/8 of the eyes. 5 out of the 8 eyes
are looking at us. And we see it right over
here-- 1, 2, 3, 4, 5. 5 of the total of 8
eyes are looking at us in a fairly creepy way.