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# Evaluating expressions with two variables: fractions & decimals

CCSS.Math:

## Video transcript

let's see if we could give ourselves some practice evaluating expressions that have two different variables in them so let's see if we can evaluate the expression 7j + 5 - 8 k when j is equal to 0.5 and k is equal to 0.25 so why don't you try to pause the video and evaluate this first before we work through it together alright so if we want to evaluate this thing everywhere where we see a J we want to replace it with a 0.5 and everywhere we see a K we want to replace it with a 0.25 so let's do that this is going to be seven times and instead of J I'm going to put a zero zero point five in there and then we have plus five minus eight times K and K we're saying is 0.25 0.25 so what is this going to be equal to so if I were to take if I were to take and I look I can color-code this seven times zero point five half of seven that's going to be three and a half three point five then I have plus five and then I'm going to subtract I am subtracting eight times 0.25 0.25 this is 1/4 I could rewrite this if I want 0.25 that's the same thing as 1/4 eight times 1/4 or another way to think about it is eight divided by four is going to be equal to two so this whole thing over here is going to be equal to two so it's going to be minus we have this minus out here so minus two and what is this going to be well let's think about it three point five plus five is eight point five minus two is going to be six point five so this is equal to this is equal to six point five let's do another one of these all right and we'll just like before try to work through it on your own before before we do it together all right now let's do it together so over here I have this expression 0.1 m plus 8 minus 12 n when M is equal to 30 and n is equal to 1/4 all right so everywhere every Ric nm I want to replace with a 30 and everywhere I see an N I want to replace with the 1/4 so this is going to be equal to 0.1 times M M is 30 times 30 plus 8 minus 12 times n where n is 1/4 and is 1/4 so what is what is 1/10 this right over here is 0.1 that's the same thing as 1/10 of 30 well 1/10 of 30 that's going to be 3 so this part is 3 then 3 plus 8 and then we're going to have - well what is 12 times 1/4 that's going to be 12 fourths or 12 divided by 4 which is going to be equal to 3 and now when we evaluate this so that is equal to this we have a 3 plus 8 minus 3 well threes are going to do a positive 3 and then you're going to subtract 3 and you're just going to be left with you're just going to be left with an 8 and you're done this expression when M is equal to 30 and N is equal to 1/4 is equal to 8