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JEE Main 20205 SeptemberMorning Shift
Exam
JEE Main
Year
2020
Date
5 September
Shift
Morning Shift
Subject
Mathematics
Chapter
Permutation and Combination

JEE Main 2020 · 5 September · Morning Shift · Mathematics · Permutation and Combination

The number of words, with or without meaning, that can be formed by...

The number of words, with or without meaning, that can be formed by taking 4 letters at a time from the letters of the word 'SYLLABUS' such that two letters are distinct and two letters are alike, is

Correct answer

240

Step-by-step solution

From the given word, S−2,L−2,A,B,Y,US - 2, L - 2, A, B, Y, U.

Number of alike letter pairs =2= 2

Number of ways to select one pair=C12= C1 2

Number of distinct letters=5= 5

Number of ways to select two distinct letters=C25= C2 5

Number of ways to arrange four letters if two are alike=4!2!= \dfrac{4 !}{2 !}

Required number of ways =C12C25⋅4!2!=2⋅10⋅242=240= C1 2 C2 5 \cdot \dfrac{4 !}{2 !} = 2 \cdot 10 \cdot \dfrac{24}{2} = 240

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