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what am I doing wrong in this equation?

I have to solve the equation to find x and check my answer each time.
equation 7(10-x)-(4-x)=48
my answer/calculations
7(10-x)-(4-x)=48
(70-7x)-(4+x)=48
70-4-7x+x=48
66-6x=48
-6x+66-66=48-66
6x=-18
6x= -18/-6 = 3
x=3
but then if I check it
7(10-3)-(4-3)=48
(70-30)-(4-3)=48
(40)-(1)=48
40-1=39

why does it equal as a minus? is there something I've done wrong for it not to equal 48
(edited 4 years ago)
Reply 1
the original equation has -7, but when you start the calculation you used 7 (instead of -7) :smile:
Original post by happily
the original equation has -7, but when you start the calculation you used 7 (instead of -7) :smile:


oh that was a typo whoops
Reply 3
Original post by justausernamee
oh that was a typo whoops


again, when you introduce 6x, it should be -6x, not 6x :smile:
watch out for minus signs hehe, very easy to make silly mistakes :smile:
you should get x=3 in the end
Original post by happily
again, when you introduce 6x, it should be -6x, not 6x :smile:
watch out for minus signs hehe, very easy to make silly mistakes :smile:
you should get x=3 in the end

If i check it I get it to equal 39 not 48..?
7(10-3)-(4-3)=48
(70-21)-(4-3)=48
(49)-(1)=48
40-1=48
(edited 4 years ago)
Reply 5
when you check such things, type directly onto your scientific calculator.
(unless ofc if you are practicing for no-calc papers haha sorry)
read your response again :smile:
7(10-3) is not equal to (70-30)
it should be 70-21
Original post by justausernamee
If i check it I get it to equal 39 not 48..?
7(10-3)-(4-3)=48
(70-30)-(4-3)=48
(40)-(1)=48
40-1=39
Original post by happily
when you check such things, type directly onto your scientific calculator.
(unless ofc if you are practicing for no-calc papers haha sorry)
read your response again :smile:
7(10-3) is not equal to (70-30)
it should be 70-21

aha thankyou!!
Hi. You did the first part correctly to get x=3, but here is where you went wrong in the second part to check it:

7(10-3)-(4-3)=48
7(7)-(1)=48
49-1=48

If you only have numbers in the parenthesis, you solve these first before multiplying from the outside. Hope this helps
Original post by justausernamee
I have to solve the equation to find x and check my answer each time.
equation 7(10-x)-(4-x)=48
my answer/calculations
7(10-x)-(4-x)=48
(70-7x)-(4+x)=48
70-4-7x+x=48
66-6x=48
-6x+66-66=48-66
6x=-18
6x= -18/-6 = 3
x=3
but then if I check it
7(10-3)-(4-3)=48
(70-30)-(4-3)=48
(40)-(1)=48
40-1=39

why does it equal as a minus? is there something I've done wrong for it not to equal 48
Reply 8
you're welcome :smile:
Original post by justausernamee
aha thankyou!!
when expanding -(4+x) you do -4+x when , should be -4-x
Original post by Hammad(214508)
when expanding -(4+x) you do -4+x when , should be -4-x


why should it be -4-x?
Original post by justausernamee
why should it be -4-x?

it is because of the negative sign in front of bracket,
so, when you expand it, it becomes:
-(4+x) = -1*4 + -1*x = -4-x
:smile:

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