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Lesson 3: Adding & subtracting rational numbers

# Adding & subtracting rational numbers: 0.79 - 4/3 - 1/2 + 150%

Sal evaluates 0.79 - 4/3 - 1/2 + 150%. Created by Sal Khan.

## Want to join the conversation?

• i dont get how he turned 550 and 450 into -100 then turned it into 137
• He Subtracted those two number and got - 100
• why did you multiplied the 100 by 3 so it become 300 ?
• this problem 1/2 −60%−25% should solve as in i have half pizza, i eat 60% of that half, then i eat 25% of whats left so i still have 0.15 of that half pizza.
why does Sal turn it into 0.5−0.6−0.25=−0.35 as the solution? and how do i know when to solve it one way and when to solve the other way?
• Well, if 1∕2 represents half a pizza, then 60% of half a pizza would be equal to 60%∙(1∕2)

But, we don't have 60%∙(1∕2), we have 60%, which we can write as 60%∙1 = 60% of a whole pizza.

And of course, taking away 60% of a pizza from half a pizza lands us at −10% of a pizza.
Taking away another quarter pizza leaves us with −35% of a pizza.
• Any reason to not write 150% as a mixed number? 1 1/2?
• You could do that, but it is easier to work with the numbers when you have it as an improper fraction. The other reason is Sal is trying to get a common denominator so that he can add/subtract all of the expressions.
• sal said alot of things that were oppisite of what he meant
• this didnt make sense make it make sense!
• i aggree
• At about in the video I don't see how 400 - 450 = (-550)

• at four minutes nine seconds how does 400 - 150 equal -550 ?