View Full Version : The wrong answer book or me: 5(z - 1) = 4(z + 4), I get z=36

tlwsmooth101

10-28-2008, 05:46 PM

5(z-1)=4(z+4)

5z-5=4z+16

5z-4z-20=16

z-20=16

z=16+20

z=36

the book says the answer is 21 and I got 36,can someone tell me whatit is that I am doing wrong.

royhaas

10-28-2008, 05:52 PM

Line 3.

Subhotosh Khan

10-28-2008, 06:53 PM

5(z-1)=4(z+4)

5z-5=4z+16

5z-4z-20=16

z-20=16

z=16+20

z=36

the book says the answer is 21 and I got 36,can someone tell me whatit is that I am doing wrong.

You can always check your answer by putting the calculated value into the original answer.

You found z = 36

Let us replace z into the left-hand-side(LHS) of the given equation:

5z -5

= 5*36 -5

= 180-5

= 175

Now the RHS

4(z+4)

= 4(36+4)

=4*40

=160

So LHS does not match RHS - so the calculated value is most probably wrong.

Check the book's answer

LHS = 5(z-1) = 5(21-1) = 5*20 = 100

RHS = 4(z+4) = 4(21+4) = 4*25 = 100

So book's answer is probably correct.............

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