Hi I have this perm and comb question where I don't really understand how to get the answer.
The question is:
How many four letter strings can be formed from the letters {a, b, c, d, e, f, g} if:
a) no repetition is allowed,
b) the strings must contain exactly two e’s,
c) the strings must contain at least two e’s.
so for b the answer was 216, I thought it would be 6x6 (because for the next 2 numbers you can select 6 choices each)
and c was 241. Can you please explain b & c to me.
The question is:
How many four letter strings can be formed from the letters {a, b, c, d, e, f, g} if:
a) no repetition is allowed,
b) the strings must contain exactly two e’s,
c) the strings must contain at least two e’s.
so for b the answer was 216, I thought it would be 6x6 (because for the next 2 numbers you can select 6 choices each)
and c was 241. Can you please explain b & c to me.