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

[tlwsmooth101]

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]

Line 3.

[Subhotosh Khan]

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.............