- #1
hms.tech
- 247
- 0
Homework Statement
A large Box of biscuits contains nine different varieties. In how many ways can four biscuits be chosen if :
a)Two are the same and the others different
b)Two each of two varieties are selected
c)three are the same and the fourth is different
Homework Equations
Combinations formulas
The Attempt at a Solution
a) The number of Choices for the first one are "9"
for the 2nd one is: "1"
for the third one are: "8"
for the fourth one are "7"
Ans : 504 (correct ans : 252 ) [How ?]
b) The number of choices for the 1st : "9"
2nd : "1"
3rd : "8"
4th : "1"
Ans : 72 (correct ans : 36) [How ?]
c) 1st choice : "9"
2nd choice : "1"
3rd Choice : "1"
4th choice : "8"
Ans : 72 (correct ans : 72) [Hmmm...]