<s>[INST] Condition for rank to be 2. Suppose that
$$\mbox{rank}\begin{equation}
\begin{pmatrix}
1 & 1 & 2 & 2\\
1 & 1 & 1 & 3\\
a & b & b & 1
\end{pmatrix}
\end{equation} = 2$$
for some real numbers $a$ and $b$. What is the value of $b$?


*

*$0.3$

*$3$

*$1$

*$0.5$


I'm unable to get the condition on $b$ only. 
 [/INST] $$\begin{equation}
\begin{pmatrix}
1 & 1 & 2 & 2\\
1 & 1 & 1 & 3\\
1/3 & 1/3 & 1/3 & 1
\end{pmatrix}
\end{equation}$$
has rank $2$ thus the closest answer is $ b=0.3$ 
</s>