In this question, there are a few kinds of the coin with a different value. To answer this question, we need to know the total coin first. The total coin count should be: 10 +20 + 15 +5= 50 coin
In this case, the coin is taken twice, that means the denominator should be 50*49. But in this question, the probablity value is 6/49, so you need to convert it into 50*49 by multiplying the numerator with 50. The value should be:
6/49 *50/50= 300/49*50
The number 300 is multiplication of 20 and 15, that mean the answer should be: 1 dimes and 1 nickles
