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# Rearranging a formula

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For the formula:

I have to make a the subject. What is the right answer? Please explain HOW you get the correct answer with working out. Thanks.

I got:
a=8-4c
44-----
444b-c

But I got the wrong answer
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(Original post by krisshP)
For the formula:

I have to make a the subject. What is the right answer? Please explain HOW you get the correct answer with working out. Thanks.

I got:
a=8-4c
44-----
444b-c

But I got the wrong answer
Its not allowed to post full solutions.

Can you show your working, then i can tell you where you went wrong.
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(Original post by krisshP)
For the formula:

I have to make a the subject. What is the right answer? Please explain HOW you get the correct answer with working out. Thanks.

I got:
a=8-4c
44-----
444b-c

But I got the wrong answer
You forgot to multiply ab by 4 when getting rid of the fraction.
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when multiplying ab by 4 I get a wrong answer of

8-4c
-------=a
4b-c

Here I first multiplied by 4 and expanded to get:
4ab-ca+4c=8
Then I -4c to get:
4ab-ca=8-4c
After this I factorised the LHS to get:
a(4b-c)=8-4c
Then I divided both sides by (4b-c) to get the answer stated above.

WHY did I fail?
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(Original post by krisshP)
when multiplying ab by 4 I get a wrong answer of

8-4c
-------=a
4b-c

Here I first multiplied by 4 and expanded to get:
4ab-ca+4c=8
Then I -4c to get:
4ab-ca=8-4c
After this I factorised the LHS to get:
a(4b-c)=8-4c
Then I divided both sides by (4b-c) to get the answer stated above.

WHY did I fail?
What is the final answer supposed to be?
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Reputation:
(Original post by krisshP)
when multiplying ab by 4 I get a wrong answer of

8-4c
-------=a
4b-c

Here I first multiplied by 4 and expanded to get:
4ab-ca+4c=8
Then I -4c to get:
4ab-ca=8-4c
After this I factorised the LHS to get:
a(4b-c)=8-4c
Then I divided both sides by (4b-c) to get the answer stated above.

WHY did I fail?

Multiply throughout by 4,
• Thread Starter
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Not sure but I know that the answer of:

8-4c
------ = a
4b-c

is wrong.

What answer do you get? Is it the same as if it is it could mean that mymaths is wrong.
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(Original post by krisshP)
Not sure but I know that the answer of:

8-4c
------ = a
4b-c

is wrong.

What answer do you get? Is it the same as if it is it could mean that mymaths is wrong.
I have indicated your mistake in my previous post.
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Thanks Raheem94 for making me learn from a mistake
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(Original post by krisshP)
Thanks Raheem94 for making me learn from a mistake
You are welcome.

By the way, what answer do you get, so that i can confirm if you are right or wrong.
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I entered the new answer on mymaths and I got a tick, so the new answer was correct
Thanks

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Updated: April 2, 2012
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