If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

# Slope, x-intercept, y-intercept meaning in context

Practice determining what each of the slope, x-intercept, and y-intercept represent in a given linear relationship.

## Want to join the conversation?

• I understand the relation between the slope and the rate, but, why the rate isn't negative if the slope is -3lit/1min? Its the same?
(8 votes)
• Well, because we need the absolute value, I reply to myself from the future haha
(61 votes)
• BIG BRAIN QUESTION, has sal ever been wrong?
(23 votes)
• You will often see correction boxes in the videos because creating these are not an easy task. There is a team who watch and correct any mistakes Sal makes as well as viewers making comments to correct the videos.
(18 votes)
• why are decimals the only accepted answer on some questions, while an improper fraction is the only accepted answer on others?! I was counted wrong when I changed 14/9 to 1.56.
(4 votes)
• Decimals are generally accepted when the number has a terminating decimal. For example, 5/4 is equal to 1.25, while 14/9 isn't equal to 1.56. If you were to divide 14/9, you would find that the five in the decimal place infinitely repeats. This is why some decimals are accepted as exact answers but not others.
(14 votes)
• I just don't get any of it z:{
(7 votes)
• Neither do I haha
(8 votes)
• Muchas gracias! No entendi nada.😎
(10 votes)
• Winston For Life.
(7 votes)
• Winston > Hopper.
(3 votes)
• As per my cathing power, I have observed in a previous video about the condition when a slope is negative, and you are saying, in this question the difference of y is negative, but according to your previous video, the difference must be positive but not negative in this question
(4 votes)
• I think that that isn't the case in this question because in the one here this shows a decrease in volume with an increase in time so it means that X and Y must have a rate of change different from each other because as the water drains the time moves on
so the difference in Y which is the liters being drained must be negative due to the water being emptied
so it is possible to have a negative change in Y
(5 votes)
• Wait so when the answers are shown, couldn't you have just divided 15 by 3?
(6 votes)
• la verdad yo ni queria estar aqui
(5 votes)
• lol deberías querer estar aquí. ¡es divertido aprender cosas nuevas!
(2 votes)
• is this representing slope?
(5 votes)

## Video transcript

- [Instructor] We're told Glen drained the water from his baby's bathtub. The graph below shows the relationship between the amount of water left in the tub in liters and how much time had passed in minutes since Glen started draining the tub. And then they ask us a few questions. How much water was in the tub when Glen started draining? How much water drains every minute? Every two minutes? How long does it take for the tub to drain completely? Pause this video and see if you can answer any or all of these questions based on this graph right over here. All right, now let's do it together. And let's start with this first question. How much water was in the tub when Glen started draining? So what we see here is when we're talking about when Glen started draining, that would be at time t equals zero. So time t equals zero is right over here. And then so how much water is in the tub? It's right over there. And this point, when you're looking at a graph, often has a special label. If you view this as the y-axis, the vertical axis as the y-axis and the horizontal axis as the x-axis, although when you're measuring time, sometimes people will call it the t-axis. But for the sake of this video, let's call this the x-axis. This point at which you intersect the y-axis that tells you what is y when x is zero? Or what is the water in the tub when time is zero? So this tells you, the y-intercept here tells you how much, in this case, how much water we started off with in the tub. And we can see it's 15 liters if I'm reading that graph correctly. How much water drains every minute? Every two minutes? Pause this video. How would you think about that? All right, so they're really asking about a rate. What's the rate at which water's draining every minute? So let's see if we can find two points on this graph that look pretty clear. So right over there at time one minute, looks like there's 12 liters in it, in the tub. And then at time two minutes, think there's nine liters. So it looks like as one minute passes, so we go plus one minute, plus one minute, what happens to the water in the tub? Well, it looks like the water in the tub goes down by, went from 12 liters to nine liters. So negative three liters. And this is a line, so that should keep happening. So if we forward another plus one minute, we should go down another three liters, and that is exactly what is happening. So it looks like the tub is draining three liters per minute. So draining three liters per minute. And so if they say every two minutes, well, if you're doing three liters per every one minute, then you're going to do twice as much every two minutes. So six liters every two minutes. Two minutes. But all of this, the second question, we were able to answer by looking at the slope. So in this context, y-intercept to help us figure out, well, where did we start off? The slope is telling us the rate at which the water in this case is changing. And then they ask us how long does it take for the tub to drain completely? Pause this video and see if you can answer that. Well, the situation in which the tub has drained completely, that means the there's no water left in the tub. So that means that our y-value, our water value is down at zero. And that happens on the graph right over there. And this point where the graph intersects the x-axis, that's known as the x-intercept. And in this context, it says, hey, at what x-value do we not have any of the y-value left? The water has run out. And we see that happens at an x-value of five, but that's giving us the time in minutes. So that happens at five minutes. After five minutes, all of the water has drained. And that makes us a lot of sense. If you have 15 liters and you're draining three liters every minute, it makes sense that it takes five minutes to drain all 15 liters.