Hi all I need some assistance 1. The problem statement, all variables and given/known data with the attempt How many 5-digit briefcase combinations contain 1. Two pairs of distinct digits and 1 other distinct digit. (e.g 12215) I wasn't sure on which approach was correct. 10 * 9 * 8 (because there are three distinct digits) or 10C2 * 5C2* 3C2 * 8 (because you have to take into account how the doubles can be orientated) 2. A pair and three other distinct digits. (e.g 27421) same issue as above 10*9*8*7 or (5C2*10) * 9 * 8 * 7 lastly I have found this question before but I couldn't get an explanation: How many ways are there to pick a collection of 12 coins from piles of pennies, nickels, dimes, quarters, and half-dollars? Base on the following condition: 1. there are only 10 coins in each pile. 16C4 - 5^2 because it's the total minus how many ways I can get from the 11th coin and the 12th coin. = 1795 2. There are only 10 coins in each pile and the pick must have at least one penny and two nickels? 1795 - 13C4(?) my logic is that it's because 12-3+4 C 4 but I'm not sure if I have to set it to 12 or 10. Thank you!