1985 AMC 12 Problem 11

Attempt Problem 11 of the 1985 AMC 12 below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 1985 AMC 12 solutions, or check the answer key.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

11.

How many distinguishable rearrangements of the letters in CONTEST have both the vowels first? (For instance, OETCNST is one such arrangement, but OTETSNC is not.)
6060
120120
240240
720720
25202520
Answer: B
Concepts:multiplication principlemultiset permutationspermutations
Small hint:
Order the two vowels in the first two positions
Big hint:
Permute the remaining five letters while accounting for the repeated TT
Solution:
The vowels O,EO,E can be ordered first in 2!2! ways. The remaining letters C,N,T,S,TC,N,T,S,T can be arranged in 5!2!=60\frac{5!}{2!}=60 distinguishable ways because the two TT’s agree. The total is 2⋅60=120.2\cdot60=120.
Thus the correct answer is B.
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