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sjs | 20:39 Mon 15th Jan 2007 | Quizzes & Puzzles
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hi can someone help me with my sons algebra homework please- i'm a bit rusty. its the pluses and minuses that are confusing me! Thanks in anticipation

a) 5-4x = 3 + x

b) 8n +11 = 1 + 6n

c) 6- x = 11 -3x

d) 7 = 3y = 5y -2

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a0 x=0.4
b)n=-5
c)x=-2
6) impossible
i think (c) is x = 2.5
6 - x = 11 - 3x
2x = 5
x = 2.5
I agree with Kettledrum, in c) x = 2.5 (I had missed the last x in the question.)
presumably (d) is either
7 + 3y = 5y - 2
9 = 2y
4.5 = y

or 7 - 3y = 5y - 2
5 = 8y
.625 ( or 5/8) = y
Just to clarify:-
a) 5-4x = 3 + x
5-3 = 4x +x
2 = 5x
x = 2/5 = 0.4

b) 8n +11 = 1 + 6n
8n - 6n = 1 -11
2n = -10
n = -10/2 = -5

c) 6 - x = 11 - 3x
3x - x = 5
2x = 5
x = 5/2 = 2.5

Wow! That took me back 40 years...
Hope this helps. Andy
a) 5 - 4x = 3 + x
reverse equation easier to have larger amount of x on the left hand side [+x > -4x]
3 + x = 5 - 4x
(add 4x to both sides)
3 + 5x = 5
(subtract 3 from both sides)
5x = 2
(divide by 5)
x =0.4

b) 8n + 11 = 1 + 6n
(subtract 6n from both sides
2n + 11 = 1
(subtract 11 from both sides)
2n = -10
(divide by 2)
n = -5

c) 6 - x = 11 - 3x
(add 3x to both sides)
6 + 2x = 11
(subtract 6 from both sides)
2x = 5
(divide by 2)
x = 2.5

d) I guess you mean - and typed = instead of +
7 + 3y = 5y -2
reverse the equation as 5y > 3y
5y - 2 = 7 + 3y
(subtract 3y from both sides)
2y - 2 = 7
(add 2 to both sides)
2y = 9
(divide by 2)
y = 4.5

The key to the above method
if you want to eliminate something from one side of the equation do the inverse (opposite of what you want to eliminate ) to both sides of the equation.
If you want to eliminate -x then add x to both sides
If you want to eliminate +5 then subtract 5 to both sides.
always trying to change the equations to something of the order 5x = 18 or 4x = 6 etc then divide to find the value of the unknown



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thanks to everyone who helped with that one!

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