Anonymous
Anonymous asked in Science & MathematicsMathematics · 1 month ago

Arrangement question?

For question 25

I have no idea to deal with, I used 1x3x2x1x1 to solve but the answer is only 130

For question 26

Actually I don’t really understand the question. Why does it mean which is painted in one??? I just can find the answer for a which is 360. For b I tried to use (6C2x6C2)/(2!x2!) but the answer is only 6. The answers for c and d are 12 and 1170

Relevance
• 1 month ago

25.

1-digit even numbers: 4 and 6

No. of 1-digit even numbers = 2

2-digit even numbers:

The units digit is "4" or "6" (₂P₁). Assign 1 of the rest 4 digits to the tens digit place (₄P₁).

No. of 2-digit even numbers = ₂P₁ × ₄P₁ = 2 × 4 = 8

3-digit even numbers:

The units digit is "4" or "6" (₂P₁). Assign 2 of the rest 4 digits to the rest 2 digit places (₄P₂).

No. of 3-digit even numbers = ₂P₁ × ₄P₂ = 2 × 12 = 24

4-digit even numbers:

The units digit is "4" or "6" (₂P₁). Assign 3 of the rest 4 digits to the rest 3 digit places (₄P₃).

No. of 3-digit even numbers = ₂P₁ × ₄P₃ = 2 × 24 = 48

5-digit even numbers:

The units digit is "4" or "6" (₂P₁). Assign the rest 4 digits to the rest 4 digit places (₄P₄).

No. of 3-digit even numbers = ₂P₁ × ₄P₄ = 2 × 24 = 48

Total no. of even numbers formed

= 2 + 8 + 24 + 48 + 48

= 130

====

26.

(a)

There are 1 red peg, 1 white peg, 1 black peg, 1 green peg, 1 blue peg and 1 yellow peg.

Out of the 6 pegs, place 4 pegs in the 4 holes (₆P₄).

Number of arrangements = ₆P₄ = 360

----

(b)

Placing 4 pegs in the 4 holes is ₄P₄. Divided by 2!2! because there are 2 red pegs and 2 white pegs.

No. of arrangements = ₄P₄/(2!2!) = 24/4 = 6

----

(c)

Placing 4 pegs into the 4 holes is ₄P₄. Divided by 2! because there are 2 red pegs.

No. of arrangements = ₄P₄/(2!2!) = 24/4 = 6

----

(d)

There are 2 red pegss, 2 white pegs, 2 black pegs, 2 green pegs, 2 blue pegs and 2 yellow pegs.

4 pegs with 2 colours:

Firstly, choose the 2 colours from the 6 colours(₆C₂). Placing 4 pegs into the 4 holes is ₄P₄. Divided by 2!2! because each pair of pegs are painted with the same colour.

No of arrangements for 4 pegs with 2 colours

= ₆C₂ × ₄P₄ / (2!2!)

= 15 × 24 / 4

= 90

4 pegs with 3 colours:

Firstly, choose 1 colour from the 6 colours for 2 pegs (₆C₁). Then, choose other 2 colours from the rest 5 colours for other 2 pegs (₅C₂). Placing 4 pegs into the 4 holes is ₄P₄. Divided by 2! because one pair of pegs are painted with the same colour.

No of arrangements for 4 pegs with 3 colours

= ₆C₁ × ₅C₂ × ₄P₄ / 2

= 6 × 10 × 24 / 2

= 720

4 pegs with 4 colours:

Choose 4 colours from the 6 colours for 4 pegs (₆C₄). Placing 4 pegs into the 4 holes is ₄P₄

No of arrangements for 4 pegs with 4 colours

= ₆C₄ × ₄P₄

= 15 × 24

= 360

Total no. of arrangements

= 90 + 720 + 360

= 1170

• User
Lv 7
1 month ago

4 and 6 are the only even numbers

and

the final digit of an even number is always an even number.

SO: you have

single digit - 2 even numbers

double digit - 4 x 2 even numbers

etc.