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Lesson 2: 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.

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• 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 ?
• Thank you, This video helped me so much! :)
• I got 100% on the math lesson that my teacher gave me before.
• 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.
• this didnt make sense make it make sense!
• How do I do it if I want to rewrite them all as decimals?
• Then you will have to divide the fractions
And divide the percents by 100
• can someone explain the whole simplifying the fractions bit, im so confused
• So you have a LARGE fraction: 80/100
To make it smaller you divide by a number.
But what number?
Well, I know that 80 and 100 are divisible by 10.
so: 80/10 divided by 10 = 8/10
Unlike whole numbers, the larger the denominator of the fraction is, the smaller the units are