Six copies of a book cost $90. How much does each copy of the book cost?
2 answers:
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To solve the two equations simultaneously using the substitution method we need to rearrange one of the equation to make either 
or 
the subject.
We can try in turn rearranging both equations and see which unknown term would have been easier to solve first
Equation
Making the subject
, dividing each term by 2
⇒ (Option 1)
Making the subject
, multiply each term by 8 gives
⇒ (Option 2)
Equation
Making the subject
, divide each term by 3
⇒ (Option 3)
Making the subject
, divide each term by 8
⇒ (Option 4)
From all the possibilities of rearranged term, the most efficient option would have been the first option, from equation with as the subject,
We can try in turn rearranging both equations and see which unknown term would have been easier to solve first
Equation
Making
Making
Equation
Making
Making
From all the possibilities of rearranged term, the most efficient option would have been the first option, from equation