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Fraction word problem: spider eyes

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

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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.