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 Post subject: nfer 11B Q 50Posted: Mon Nov 24, 2008 1:17 pm

Joined: Fri Nov 07, 2008 11:15 am
Posts: 43
(21 x 55) + 20 = 1175

Which of the following is correct?

A) 1175 - 20 = 21 x 55
B) 21 x (55+20) = 1175
C) 1175 = 20 + (21 x 55)
D) 20 = 1175 - (21 x 55)
E) (21 x 55) + 21 = 1176

What is the easiest way of answering this? My daughter substitutes each number to create a formula that works i.e.

(1 x 2) + 3 = 5 and then replaces these numbers within each of the formulas above to see which works? She got the right answer but not sure whether her method would work with nfer 11D, Q43:

x + 3y = 2z

Which of the following is incorrect?

A) 2x + 6y = 4z
B) 3y = 2z - x
C) x + 3y - 2z = 0
D) 2z - 3y = x
E) 2x = 4z + 6y

Not sure about the best method here (although she managed to get this one right too - maybe I should just leave her to do it her way!)

Any suggestions from the maths brains out there?

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 Post subject: Posted: Mon Nov 24, 2008 3:10 pm

Joined: Tue Jan 01, 2008 1:05 pm
Posts: 515
I assume you should be looking for the incorrect one, and not the correct one.

Basic rule is that what you do to one side of the =, you do to the other side.

e.g if an x disappears (i.e is subtracted) from one side, it is added to the other side. If the variables ar doubled on one side, they are doubled on the opposite side.

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 Post subject: Posted: Mon Nov 24, 2008 3:16 pm

Joined: Tue Jan 01, 2008 1:05 pm
Posts: 515
To add further, do not need to start substituting values. Each of these really is a 5 second question. For example, just moving the variables around cannot change 21x55 to somehow give 55+20, so should be able to see B is the correct answer.

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 Post subject: Re: nfer 11B Q 50Posted: Mon Nov 24, 2008 4:05 pm

Joined: Thu Nov 02, 2006 3:07 pm
Posts: 1149
Location: Finchley - Barnet
Quote:
x + 3y = 2z

Which of the following is correct?

A) 2x + 6y = 4z
B) 3y = 2z - x
C) x + 3y - 2z = 0
D) 2z - 3y = x
E) 2x = 4z + 6y

The only INcorrect answer is E!

_________________
sj355

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 Post subject: Posted: Mon Nov 24, 2008 5:06 pm

Joined: Fri Nov 07, 2008 11:15 am
Posts: 43
Sorry, there was me trying to copy the entire question out correctly to make it easy to understand! Have edited message from 'correct' to 'incorrect'.
I agree the second question is the easiest to work out just by looking.

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