Question : The cost of 12 apples and 15 oranges is INR 660. The cost of 15 apples and 21 oranges is INR 870. Find the cost of one apple.
Option 1: INR 25
Option 2: INR 15
Option 3: INR 30
Option 4: INR 20
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Correct Answer: INR 30
Solution :
Let the cost of one apple be $x$ and one orange be $y$.
According to the question,
$12x+15y=660$ .......(1)
And, $15x+21y=870$ ........(2)
Multiplying equation (1) by 5 and equation (2) by 4, we get,
$60x+75y = 3300$ and $60x+84y=3480$
Subtracting these equations, we get,
$75y-84y=3300-3480$
⇒ $9y=180$
⇒ $y=20$
Putting this value in (1), we get,
$12x+15(20)=660$
⇒ $12x+300=660$
⇒ $12x = 360$
⇒ $x=30$
⇒ The cost of one apple is INR 30
Hence, the correct answer is INR 30.
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