Study on the flyACTMathematicsCounting, combinations, and permutations

Counting, combinations, and permutations — ACT practice questions

Practice 43 Counting, combinations, and permutations questions in the app

What this topic is

Counting, combinations, and permutations on the ACT Mathematics test covers how many ways objects can be selected or arranged, including overlapping sets, unordered groups, and sequences that may contain repeated items.

A student must find how many people belong to at least one category after adjusting for those in both, distinguish choosing a pair from listing ordered lineups, and count distinct rearrangements of letters when some letters repeat. Questions typically appear as short word problems with a single numeric result among five answer choices.

Common traps include double-counting the overlap, using permutations when order does not matter, and treating identical letters as if they were all different.

Sample questions

Pick an answer to see whether it is right — nothing is saved, and nothing needs an account.

Question 1Mid

How many distinct arrangements can be made using all the letters in the word LEVEL?

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Answer: C — 30

LEVEL has 5 letters with LL repeated twice and EE repeated twice. The number of distinct arrangements is 5!2!2!=1204=30\dfrac{5!}{2!\,2!}=\dfrac{120}{4}=30.

Question 2Mid

Naomi will attend 2 of 9 workshops. How many different pairs of workshops can she choose?

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Answer: B — 36

The order of the 2 selected workshops does not matter, so use a combination. There are (92)=36\binom{9}{2}=36 selections.

Question 3Easier

Of 50 students, 26 joined robotics, 18 joined drama, and 7 joined both groups. How many students joined at least one of the groups?

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Answer: C — 37

Adding the two group counts includes the 7 students in both groups twice. Inclusion-exclusion gives 26+187=3726+18-7=37.

Every question is picked for where you are right now, wrong answers come back until they stick, and it all works offline.

Practice 43 Counting, combinations, and permutations questions in the app

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