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please could someone help me get and understand this maths question?

(77 Posts)
ssd Wed 05-Oct-11 16:17:54

thanks, cant work it out at all

solve.

3a=3a-6 and a
... ....... ...
4 2 3

(the ... is meant to be a line, the "and" is a plus sign)

thanks

ssd Wed 05-Oct-11 16:19:58

sorry, means

3a over 4 = 3a minus 6 over 2 + a over 3

MrsWobble Wed 05-Oct-11 16:21:49

a = 3, you need to multiply everything by 12 to get rid of the fractions and then rearrange it to work it out.

AMumInScotland Wed 05-Oct-11 16:21:55

I'm not understanding where the "4 2 3" at the bottom fits in - is that meant to be part of an equation? The top bit works on its own

3a = 3a - 6 + a

subtract 3a from each side

0 = -6 + a

add 6 to each side

6 = 6 - 6 + a

get rid of the + and - 6 on the right

6 = a

so a=6

Make any sense?

AMumInScotland Wed 05-Oct-11 16:22:37

ok mine makes no sense now smile

AMumInScotland Wed 05-Oct-11 16:24:25

What MrsWobble says - when you have lots of fractions with different things on the bottom, you have to find something to multiply all the pieces by to make the fractions go away, then work from there.

So since you have things over 2,3,and 4, multiplying by 12 will make it much simpler to solve

ssd Wed 05-Oct-11 16:30:09

thanks

i know i'm being annoying,but could someone possibly write it out for me the way you would in an exam?

sorry still am stuck

ssd Wed 05-Oct-11 16:38:34

when i multiplied it all out by 12 i got 9a over 12 = 18a over 12???

wellwisher Wed 05-Oct-11 16:44:35

multiply all by 12 and you get this:

36a = (36a-72)+12a

which can be simplified to 36a = 48a -72

which means that 72 = 12a

which means that a = 6 (72 divided by 12)

nickelbabe Wed 05-Oct-11 16:47:57

3a over 4 = 3a minus 6 over 2 + a over 3

3a/4 = (3a-6)/2+ a/3

I know that's not the answer, it's just a neater way to write the question.

and I suddenly realised that I'm too tired in the brain to work it out sad

AMumInScotland Wed 05-Oct-11 16:48:52

3a/4 = 3a - 6/2 + a/3

multiply each bit by 12 -

3ax12/4 = 3ax12 - 6x12/2 + ax12/3

divide out the numbers where you can -

9a = 36a - 36 + 4a

sort out the a's on each side -

9a = 40a - 36

take away 9a from each side -

0 = 31a - 36

take away 36 from each side -

36 = 31a

divide both sides by 31 -

36/31 = a

you'll have to turn the /s into proper lines but you should be able to see where they belong?

Having done all that, I'm not sure if I've got the original question right - it seems odd having 6 over 2 as part of any equation, as you wouldn't usually put it like that. Can you see my working anyway?

schobe Wed 05-Oct-11 16:52:34

I reckon nickelbabe's translation of the original question is probably right, though it doesn't give a nice answer which can be suspicious with some 'sanitised' maths teaching.

Multiplying through by 12 gives 9a = 18a - 36 + 4a
So 13a = 36
a = 36/13

schobe Wed 05-Oct-11 16:53:56

I REALLY don't mean any offence by this, but wellwisher's answer may confuse you because she hasn't seen the denominators when multiplying through by 12.

wellwisher Wed 05-Oct-11 16:54:09

I think mine is wrong, actually. Ignore blush

schobe Wed 05-Oct-11 16:55:29

grin

Toomanyworriedsonhere Wed 05-Oct-11 17:00:48

Finally - Schobe you have the same as me.
Hurrah for us - clearly we are right unless we've misunderstood the question!

Toomanyworriedsonhere Wed 05-Oct-11 17:03:23

I kept redoing it thinking it should have a nice simple answer but since mine matches yours we must both be right.

What age level is this?

AMumInScotland Wed 05-Oct-11 17:06:46

What others have said, but with the working bit by bit -

3a/4 = (3a - 6)/2 + a/3

multiply each bit by 12 -
3ax12/4 = 12(3a - 6)/2 + ax12/3

divide out the numbers where you can -
9a = 6(3a - 6) + 4a

get rid of the brackets -
9a = 18a - 36 + 4a

sort out the a's on each side -
9a = 22a - 36

take away 9a from each side -
0 = 13a - 36

add 36 to each side -
36 = 13a

divide both sides by 13 -
36/13 = a

activate Wed 05-Oct-11 17:09:09

so 3a-6+a = 3a

so 3a-6=3a-a = 2a

so 3a=2a+6
so 3a-2a=6
so a=6

so 3x6 -6 +6 = 18-6+6 = 18 = 3 x 6

pickledsiblings Wed 05-Oct-11 17:09:39

i get the same as amum

activate Wed 05-Oct-11 17:10:11

didn't see the fraction

lost the will to live

AMumInScotland Wed 05-Oct-11 17:14:03

I think we've settled on -

3a/4 = (3a - 6)/2 + a/3

as the question - that would fit with the length of the .... lines on the original too, which I hadn't taken into account first time round grin

pickledsiblings Wed 05-Oct-11 17:20:01

a = 36/13 i mean

ssd Wed 05-Oct-11 18:02:37

sorry am more confused now grin

is a=6 or is it a=3

its age 13 homework BTW

Toomanyworriedsonhere Wed 05-Oct-11 18:04:10

a is not 6 or 3.
If the orignal question is as written by AMumInScotland her solution explains it clearly.
a is 36/13

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