SATMathematics Practice Test 1

The value 108 in the equation is the value of P in $\mathit{P}=108-23\mathit{d}$ when $\mathit{d}=0$. When $\mathit{d}=0$, Kathy has worked 0 days that week.
In other words, 108 is the number of phones left before Kathy has started work for the week.
Therefore, the meaning of the value 108 in the equation is that Kathy starts each week with 108 phones to fix because she has worked 0 days and has 108 phones left to fix.
Choice A is incorrect because Kathy will complete the repairs when $\mathit{P}=0$.
Since $\mathit{P}=108-23\mathit{d}$, this will occur when $0=108-23\mathit{d}$ or when$\mathit{d}=\frac{108}{23}$ ,not when $\mathit{d}=108$.
Therefore, the value 108 in the equation does not represent the number of days it will take Kathy to complete the repairs.
Choices C and D are incorrect because the number 23 in $\mathit{P}=108-23\mathit{P}=108$ indicates that the number of phones left will decrease by 23 for each increase in the value of d by 1;
in other words, that Kathy is repairing phones at a rate of 23 per day, not 108 per hour (choice C) or 108 per day (choice D).