Permutations and Combinations: Arrangement of Identical Cans
Published on September 25, 2026
Calculate the number of arrangements for 7 identical cans under specific conditions by treating groups of identical items as single blocks. The solution covers both restricted end positions and grouped item constraints.
Question
Answer
Problem 10
(i) the first and last cans in the row are the same type of drink.
(ii) the 3 cans of cola are all next to each other and the 2 cans of green tea are not next to each other.
Solution
Part (i): The first and last cans are the same type of drink.
Remaining cans to arrange in the middle:
Number of arrangements =
Remaining cans to arrange in the middle:
Number of arrangements =
Remaining cans to arrange in the middle:
Number of arrangements =
Part (ii): The 3 cans of cola are all next to each other and the 2 cans of green tea are not next to each other.
Let the block of colas be
The items to arrange are now:
Total arrangements of
Treat the two green teas as a single block
The items to arrange are now:
Number of arrangements of
Number of arrangements = (Total with
Number of arrangements
(i) 50
(ii) 18