A bag contains coins of one rupee, two rupee & five rupees. The total money in the bag is Rs. 120. If the total number of one rupee and two rupee coins are 35 and in ratio of coins is 2 : 5. Find the probability of getting a 5 rupee coin if a coin is randomly picked from the bag?
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$12/47$
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$21/46$
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$12/37$
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$21/37$
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None of these
A
Correct answer
Explanation
One rupee and two rupee coins total 35 in ratio 2:5, so one rupee = 10 coins and two rupee = 25 coins. Their value = 10 + 50 = Rs 60. Remaining Rs 60 is from five rupee coins, so 12 five rupee coins. Total coins = 10 + 25 + 12 = 47. Probability of 5 rupee coin = 12/47. The key is working backwards from the ratio and total value.