There are seven nickels and six dimes in your pocket. You randomly pick a coin out of your pocket and place it on a counter. Then you randomly pick another coin. Both coins are nickels.

Question

There are seven nickels and six dimes in your pocket. You randomly pick a coin out of your pocket and place it on a counter. Then you randomly pick another coin. Both coins are nickels.

Answer 1

In an effort to vary the type of problems, math teachers often pose such problems. Anyone who doesn't know the difference between a nickel and a dime simply by feel has some major difficulties. There is nothing random about choosing a coin in a pocket with dimes and nickels in it.

I would much prefer this practice be permanently halted. The same problem theory can be presented by using say red and yellow plastic chips of the same size, weight, shape, and texture. It might be boring, but it would certainly be realistic.

Answer 2

Hi Larry,

What is the question? Is it to find the probability of getting two nickels? In this case, you need to use the Multiplication Rule, but keep in mind that you removed a coin and a nickel after first draw. Let's designate getting a nickel on the first draw N1 and the second draw N2:

P(N1) = 7/13 (7 nickels available out of 13 total coins)

P(N2) = 6/12 = 1/2 (6 nickels available out of 12 total coins)

Remember, we subtracted one total coin and one nickel to account for first draw:

P(N1 and N2) = (7/13) * (1/2)

P= 0.269

I hope this helps.