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# One-step subtraction equations

CCSS.Math:

## Video transcript

solve for a and check your solution we have a plus five is equal to 54 now all this is saying is that we have some number some variable a and if I add 5 to it I will get 54 and you might be able to do this in your head but we're going to do it a little bit more systematically because that'll be helpful for you when we do more complicated problems so in general whenever you have an equation like this we want to have the variable we want this a all by itself on one side of the on one side of the equation we want to isolate it it's already on the left-hand side so let's try to get rid of everything else on the left-hand side well the only other thing on the left-hand side is this positive five well the best way to get rid of a plus five or of a positive five is to subtract five so let's subtract five but remember this says a plus five is equal to 54 if we want the Equality to still hold anything we do to the left-hand side of this equation we have to do to the right side of the equation so we also have to subtract 54 from the right so we have a plus five minus five well that's just going to be a plus zero because you add five and you subtract five they cancel out so a plus 0 is just a and then 54 minus 5 that is 49 and we're done we have solved for a a is equal to 49 and now we can check it and we can check it by just substituting 49 back for a in our original equation so instead of writing a plus five is equal to 54 let's see if 49 plus five is equal to 54 so we're just substituting it back in 49 49 plus let me do that in that same shade of green 49 plus five is equal to 54 we're trying to check this 49 plus five is 54 and that indeed is equal to 54 so it all checks out