The cost of one pen is Rs 15.
<h3>How to find the cost of one pen?</h3>
It is given that Ruby paid with a 500 rupee note and got Rs 90 back.
This means that she spent 410 rupees.
Therefore the cost of 24 books and 5 pens is Rs 410.
Let the cost of books be x and the cost of pens be y.
Therefore, we can form the following equations:
24x + 5y = 410 (1)
12x + 10y = 280 (2)
We have to find the value of y.
Multiply the second equation by 2:
24x + 20y = 560 (3)
Now subtract the first equation from the third equation:
24x + 20y - 24x - 5y = 560 - 410
15y = 150
y = 15.
The variable y represents the cost of one pen.
This means that the cost of one pen is Rs 15.
Therefore, we have found that the cost of one pen is Rs 15.
Learn more about solving a system of equations here: brainly.com/question/13729904
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