Day 21 of 60 · Tue 20 Oct · Daily workbook · CAT in 40 days

Day 21: Permutations, Probability & Sets + Math Puzzle Set + Economics & Business RC

Day 21 of the free ThinkCAT 60-day CAT challenge: 5 permutations, probability & sets questions and 3 spaced-review QA questions, a full math puzzle DILR set (4 questions), a economics & business RC passage (4 questions), plus para summary and sentence placement. Every question is a real CAT PYQ.

QA · 8
DILR · 4
VARC · 6
40 minutes
Real CAT questions

Concept card

Permutations, Probability & Sets

Core formulas

Independent choices multiply (and); separate cases add (or)
Circular arrangements: (n − 1)!; identical items: n!/(p! q!)
n identical items to k people, each ≥ 1: C(n − 1, k − 1)
P(at least one) = 1 − P(none); n(A ∪ B) = n(A) + n(B) − n(A ∩ B)

60-second shortcut · Go through the complement

At least one six in 3 throws: 1 − (5/6)³ = 91/216.

Trap box

Looks like: 6 people around a table: 6! waysActually: Fix one seat: 5! = 120
Looks like: At least one head in 3 tosses = 3 × ½Actually: 1 − (½)³ = 7/8

From the free Modern Math Formula Sheet (PDF).

What's in Day 21

QA: Permutations, Probability & Sets (5) + 3 spaced-review questions
DILR: Math Puzzle set, 4 questions
RC: Economics & Business passage
VA: Para Summary, Sentence Placement

Year, slot and question number for each question appear with the answer key after you submit.

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