The equation to represent the age of a dog in people years is p=6(d-1)+21 where p represents the age of a dog in people years, and d represents its age in dog years. How old is a dog if he is 17 in people years?

Oct 23, 2016

$d = \frac{1}{3} \text{ year or 4 months old}$

Explanation:

You are TOLD that $p = 17$ and ASKED to find the value of $d$

Substitute for $p$ and then solve for $d$

$p = 6 \left(d - 1\right) + 21$

$17 = 6 \left(\textcolor{red}{d} - 1\right) + 21 \text{ }$ subtract 21 from each side.

$17 - 21 = 6 \left(\textcolor{red}{d} - 1\right)$

$- 4 = 6 \textcolor{red}{d} - 6 \text{ } \leftarrow$ add 6 to both sides.

$- 4 + 6 = 6 \textcolor{red}{d}$

$2 = 6 \textcolor{red}{d}$

$\frac{2}{6} = \textcolor{red}{d}$

$d = \frac{1}{3} \text{ year or 4 months old}$