Suppose variables
\[A, \;\]
are measured and take the values \[(A,B)=(20,35), \; (30, 60)\]
.It is required to find the value of
\[B\]
at \[A=23\]
. Using the linear model\[\frac{B-B_1}{A-A_1}=\frac{B_2-B_1}{A_2-A_1}\]
gives
\[\frac{B-35}{23-20}=\frac{60-35}{30-20} \rightarrow B= \frac{60-35}{30-20} \times (23-20)+35=42.5\]