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#### Please solve RD Sharma class 12 chapter Algebra of matrices exercise 4.3 question 73 maths textbook solution

Answer: Amount spent on X=Rs 3400 Amount spent on Y=Rs 7200

Hint: Matrix multiplication is only possible, when the number of columns of first matrix is equal to the number of rows of second matrix.

Given:

$A=\left[\begin{array}{c} 40 \\ 100 \\ 50 \end{array}\right]$

The number of contacts of each type made in two cities X and Y is given in matrix B as

$B=\left[\begin{array}{ccc}1000 & 500 & 5000 \\ 3000 & 1000 & 10000\end{array}\right] \begin{array}{c}X \\Y \end{array}$

Total amount spent by the group on the two cities X and Y can be given by.

$\\B A=\left[\begin{array}{ccc}1000 & 500 & 5000 \\ 3000 & 1000 & 10000\end{array}\right]\left[\begin{array}{c}40 \\ 100 \\ 50\end{array}\right]\\\\ =\left[\begin{array}{c}40000+50000+250000 \\ 120000+100000+500000\end{array}\right]\\\\ =\left[\begin{array}{l}340000 \\ 720000\end{array}\right]$

As we know 100 paise=Rs 1

Hence,

Amount spent on X=Rs 3400

Amount spent on Y=Rs 7200