Question 445895
.
7 audio cassettes and 3 video cassettes cost rs 1110,while 5 audio cassettes and 4 video cassettes cost rs 1350 
find the cost of an audio cassette and a video cassette
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        In the post by @mananth the solution is incorrect, since equations are written incorrectly.

        I came to do the job accurately.



<pre>
Audio --- x Cost
Video --- y Cost

Equations

    7x + 3y = 1110    (1)

    5x + 4y = 1350    (2)


I will solve using the determinant method (= Cramer's method),
sinse it is easier to write (no need to write excessive words).


D (the determinant) is         7*4 - 5*3 = 28 - 15 = 13.

Dx (the determinant for x) is  1110*4 - 1350*3 = 390.

Dy (the determinant for y) is  7*1350 - 5*1110 = 3900.


Hence,  x = Dx/D = 390/13 = 30;  y = Dy/D = 3900/13 = 300.


<U>ANSWER</U>.  Audio-cassette costs rs 30;  video-cassette costs rs 300.


<U>CHECK</U>. First  equation, left side is  7*30 + 3*300 = 1110.   ! correct !

       Second equation, left side is  5*30 + 4*300 = 1350.   ! correct !
</pre>

Solved correctly.