Weird answer for "Solving systems of linear equations" in SAT math section – Khan Academy Help Center - Hungarian (BETA)

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vchamp44

2018. február 26. 22:34
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This was the math problem.

1.5a - 4.5b = 3(a + b)

5.5b = 5(b - a) + 2.5a

Consider the system of equations above. If (a,b) is the solution to the system, then what is the value of b - a?

This is the solution Khan Academy gave.

A part of the solution confused me. I understood how they reached 5.5b = 30b - 12.5b, but I don't understand how b = 0. Shouldn't b = 12?

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Iksha Handa

2018. február 27. 4:00
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So after 5.5b = 30b -12.5b the equation simplifies to

5.5b = 17.5b

-17.5b = -17.5b Then bringing the 'b's to one side you have

-12b = 0

or alternatively 0 = 12b (by subtracting 5.5b from both sides)

0 divided by any number is 0 so b = 0
vchamp44

2018. február 28. 16:09
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Gotcha. So were dividing both sides by -12. I thought we were adding +12 to both sides to get b = 12.

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