math question. i need help!

Test Preparation SAT Preparation
1

<p>tx + 12y = -3.
the equation above is the equation of a line in the xy-plane, and t is a constant. if the slope of the line -10, what is the value of t?</p>

<p>this is what i did:
isolated y so y= -tx/12 -(1/4)
slope is -10 so
-10 = -t/12 - (1/4)
add (1/4) to both sides so
-9.75 = -t/12
t= 117
however, the answer key says it's 120. i checked the explanation, and this is what it says:
The correct answer is 120. If the given equation is put into slope-intercept form, y=mx+b, the slope will be the value of m (that is, the coefficient of x). Rewriting tx +12y = -3 to get y by itself on one side of the equation gives 12y=-tx-3 and y= -tx/12 - 1/4. Since the slope of the line is -10, it follows that -t/12=-10. Solving this last equation for gives 120.</p>

<p>my question is, where did the 1/4 go? is it the error of the answer key or me? thanks in advance!</p>

2

<p>I’m not sure completely, but it seems like as if the 1/4 is not needed for the answer. All they are asking is for you to solve T. And you solved it as 120, they are not asking you to solve the question but for only the slope which is</p>

<p>-t/12=-10 , thus t+120</p>

3

<p>oh i see now. thanks a ton!</p>