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Lesson 4: Rational number word problems

# Rational number word problem: checking account

Your checking account is overdrawn. Not good. Use your knowledge of decimals and adding negative and positive numbers to bring your account back into the black. Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

• Can't I just subtract 15.08 from 100.00, add 426.90, and get the same answer?
• Yes, and this is just because you have a list of positive and negative numbers that you are adding, you can always change the order when adding signed numbers.
• I love this math program, but I feel the videos are sometimes much easier than the practices.
• super video just I dont really know how he got that at ?
• Forget the fluff, think in terms of arithmetic, but use the \$ to complete the equation. -15.08 + 526.90. Start on right on the number line, -15.08 then add (mover left on the number line) 526.90. But the easiest way is to subtract -15.08 from 526.90 to get 511.82. The answer then is \$511.82.
• At , he uses a Kerala Marlboro line. How does that work?
• Well... he shows that you start out with less than 0. Before you can add the 526.90, you have to pay off your debt first. Hope this helps, like if you agree!
• Can someone help me out.
!.I don't know how to do this
2.What does rational mean?(JK)
• A rational number is one that can be written as a ratio. So if you have the number 8, that can be written as 8 over 1.
• why would he keep adding them up if he already has a - number
• if y=2x-3 what is y when y is 5 how do you go about fing the answer to this kind of problem
• Did you mean when y is 5, what is x?
In that case, plug 5 in for y, and get x by itself.
5=2x-3
Add 3 to both sides (moves -3)
8=2x
Divide both sides by two, and you get your answer of 4=x.
• At Sal mentions that Stewart has a negative amount of money in his account; how is that possible?

Is it because he's in debt?
• It is impossible to achieve a negative amount of money in your account unless you take something that isn't yours. So to answer your question, yes, it means he is in debt
• how do you go negative in your bank account
• It's called being overdrawn. The bank allows you to take out more money than you have, which means you go 'negative' or go into the red.
At this point you owe the bank the money that is the equivalent of the negative amount in your account (plus any extra charges the bank makes you pay).
For example, if I have \$200.00 in the bank and spend \$300.00 (assuming the bank allows me to do this) then I am now \$100.00 in the red, which I owe back to the bank.
• where did the 526.90 come from at ? did he add the numbers did not hear him say
• Yes, he added two deposits, one of \$426.90 and another one of \$100.00

## Video transcript

At the beginning of the week, Stewart's checking account had a balance of negative \$15.08. On Monday morning, he deposited a check for \$426.90. On Tuesday morning, he deposited another check for \$100. How much was in Stewart's checking account after the second deposit, so after both of these deposits right over here. So he starts off with a negative balance. So a negative balance means that he's overdrawn his checking account. He actually owes the bank money now. Luckily, he's now going to put some money in his bank account. So he'll actually have a positive balance in his checking account. So he's starts off with the negative \$15.08. And then to that, he adds \$426.90. And then he adds another \$100. So he started off with negative \$15.08. And then to that, he adds \$426.90 and \$100. So that's \$526.90. And so how much is going to have in his bank account? He started owing \$15.08, and then he's going to add \$526.90. So one way to visualize it is, if you think about it on a number line, if this is 0 right over here, he's going to start off at negative \$15.08. But then he's going to add \$526. So this right over here, this is \$15.08 to the left. That's how much he owes. And to that, he's going to add \$526. So I'm not drawing this to scale. But to that, he is going to add \$526.90. So the amount that he's going to be in the positive is going to be \$526.90 minus the \$15.08. It's essentially going to be this length right over here. That's how much he's going to be in the positive. And that's going to be \$526.90 minus \$15.08. So that's going to be, and we can even just rewrite this so it actually looks exactly like that. That's exactly the same thing as \$526.90 minus-- adding a negative is the same thing as subtracting a positive-- minus \$15.08. And this is-- I will do this in another color-- \$526.90 minus \$15.08. Let's see, 0 is less than 8. Let's make that a 10 and borrow from this 9. So that becomes an 8, or I guess you could say we're regrouping. Now, everything up here is larger than everything there. So 10 minus 8 is 2. 8 minus 0 is 8. We have our decimal. 6 minus 5 is 1. 2 minus 1 is 1. And then you have 5 minus nothing. So he is left with \$511.82 after his second deposit.