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How many ways can 12 boys be seated around a round table if two particular boys must sit together? 2. How many ways can six board of directors be seated on a circular table?

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2 parts
a

16x4−96x3+216x2−216x+8116x^4 - 96x^3 + 216x^2 - 216x + 81

b

x3−6x2+12x−8x^3 - 6x^2 + 12x - 8

Step-by-step solution

6 steps

Here are the solutions to your assignment questions:

1. Seating 12 boys around a round table with 2 particular boys together

Step 1: Treat the 2 particular boys who must sit together as a single unit.
This reduces the number of entities to arrange to (12−2)+1=11(12 - 2) + 1 = 11 units.

Step 2: Calculate the number of ways to arrange these 11 units around a circular table.
For circular permutations, the number of ways to arrange nn distinct items is (n−1)!(n-1)!.
So, for 11 units, the number of arrangements is (11−1)!=10!(11-1)! = 10!.

10!=3,628,80010! = 3,628,800

Step 3: Account for the arrangements of the 2 particular boys within their unit.
The 2 boys can sit in 2!2! ways within their unit (Boy A then Boy B, or Boy B then Boy A).

2!=2×1=22! = 2 \times 1 = 2

Step 4: Multiply the arrangements from Step 2 and Step 3 to get the total number of ways.
Total ways = (arrangements of units) ×\times (arrangements within the unit)

3,628,800×2=7,257,6003,628,800 \times 2 = 7,257,600

The 2 particular boys must sit next to each other in 7,257,600 ways\boxed{\text{7,257,600 ways}}.

2. Seating six board of directors on a circular table

Step 1: Identify the number of people to be arranged.
There are n=6n=6 directors.

Step 2: Apply the formula for circular permutations.
The number of ways to arrange nn distinct items in a circle is (n−1)!(n-1)!.

(6−1)!=5!(6-1)! = 5!

Step 3: Calculate the factorial.

5!=5×4×3×2×1=1205! = 5 \times 4 \times 3 \times 2 \times 1 = 120

Six board of directors can sit on a circular table in 120 ways\boxed{\text{120 ways}}.

3. Expand the given expressions

Part a· 3 steps

Expand (2x−3)4(2x-3)^4

  1. Use the binomial theorem (a+b)n=∑k=0n(nk)an−kbk(a+b)^n = \sum_{k=0}^{n} \binom{n}{k} a^{n-k} b^k.

    Here, a=2xa=2x, b=−3b=-3, and n=4n=4.

  2. Calculate each term of the expansion.

    Term 1 (k=0k=0): (40)(2x)4(−3)0=1⋅(16x4)⋅1=16x4\binom{4}{0}(2x)^4(-3)^0 = 1 \cdot (16x^4) \cdot 1 = 16x^4
    Term 2 (k=1k=1): (41)(2x)3(−3)1=4⋅(8x3)⋅(−3)=−96x3\binom{4}{1}(2x)^3(-3)^1 = 4 \cdot (8x^3) \cdot (-3) = -96x^3
    Term 3 (k=2k=2): (42)(2x)2(−3)2=6⋅(4x2)⋅9=216x2\binom{4}{2}(2x)^2(-3)^2 = 6 \cdot (4x^2) \cdot 9 = 216x^2
    Term 4 (k=3k=3): (43)(2x)1(−3)3=4⋅(2x)⋅(−27)=−216x\binom{4}{3}(2x)^1(-3)^3 = 4 \cdot (2x) \cdot (-27) = -216x
    Term 5 (k=4k=4): (44)(2x)0(−3)4=1⋅1⋅81=81\binom{4}{4}(2x)^0(-3)^4 = 1 \cdot 1 \cdot 81 = 81

  3. Sum the terms to get the expanded form.

    (2x−3)4=16x4−96x3+216x2−216x+81(2x-3)^4 = \boxed{16x^4 - 96x^3 + 216x^2 - 216x + 81}

Part b

x3−6x2+12x−8x^3 - 6x^2 + 12x - 8

Expand (x−2)3(x-2)^3* (Based on your notes for Question 2, where a=xa=x, b=−2b=-2, A=3A=3)

  1. Use the binomial theorem (a+b)n=∑k=0n(nk)an−kbk(a+b)^n = \sum_{k=0}^{n} \binom{n}{k} a^{n-k} b^k.

    Here, a=xa=x, b=−2b=-2, and n=3n=3.

  2. Calculate each term of the expansion.

    Term 1 (k=0k=0): (30)(x)3(−2)0=1⋅x3⋅1=x3\binom{3}{0}(x)^3(-2)^0 = 1 \cdot x^3 \cdot 1 = x^3
    Term 2 (k=1k=1): (31)(x)2(−2)1=3⋅x2⋅(−2)=−6x2\binom{3}{1}(x)^2(-2)^1 = 3 \cdot x^2 \cdot (-2) = -6x^2
    Term 3 (k=2k=2): (32)(x)1(−2)2=3⋅x⋅4=12x\binom{3}{2}(x)^1(-2)^2 = 3 \cdot x \cdot 4 = 12x
    Term 4 (k=3k=3): (33)(x)0(−2)3=1⋅1⋅(−8)=−8\binom{3}{3}(x)^0(-2)^3 = 1 \cdot 1 \cdot (-8) = -8

  3. Sum the terms to get the expanded form.

    (x−2)3=x3−6x2+12x−8(x-2)^3 = \boxed{x^3 - 6x^2 + 12x - 8}
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