Q.There are two book shops owned by Suresh and Ganesh. Their sales (in Rupees) for books in three subjects — Physics, Chemistry and Mathematics — for two months, July and August 2017, are given by two matrices A and B. July sales (Physics, Chemistry, Mathematics): $A = \begin{bmatrix} 5600 & 6750 & 8500 \\ 6650 & 7055 & 8905 \end{bmatrix}$ (first row Suresh, second row Ganesh). August sales (Physics, Chemistry, Mathematics): $B = \begin{bmatrix} 6650 & 7055 & 8905 \\ 7000 & 7500 & 10200 \end{bmatrix}$ (first row Suresh, second row Ganesh). Find the increase in sales in Rupees from July to August 2017.

Given July sales $A = \begin{bmatrix} 5600 & 6750 & 8500 \\ 6650 & 7055 & 8905 \end{bmatrix}$ and August sales $B = \begin{bmatrix} 6650 & 7055 & 8905 \\ 7000 & 7500 & 10200 \end{bmatrix}$ (Row 1 = Suresh, Row 2 = Ganesh; columns = Physics, Chemistry, Mathematics).

The increase in sales is $B-A$:

Suresh: Physics $6650-5600=1050$; Chemistry $7055-6750=305$; Mathematics $8905-8500=405$

Ganesh: Physics $7000-6650=350$; Chemistry $7500-7055=445$; Mathematics $10200-8905=1295$ …

Subtract the July sales matrix A from the August sales matrix B entry-by-entry to get …

• Computing $A-B$ (a decrease) instead of $B-A$ (the increase asked for). …