How many two digits number can be formed from the digits 3 5 7 and 9 if repetition is not allowed?

Problem 1: How many 3-digit numbers can be formed from the digits 1, 2, 3, 4 and 5 assuming that – 

(i) repetition of the digits is allowed?

Solution: 

Índice

• Problem 1: How many 3-digit numbers can be formed from the digits 1, 2, 3, 4 and 5 assuming that – 
• (i) repetition of the digits is allowed?
• (ii) repetition of the digits is not allowed? 
• Problem 2: How many 3-digit even numbers can be formed from the digits 1, 2, 3, 4, 5, 6 if the digits can be repeated?
• Problem 3: How many 4-letter code can be formed using the first 10 letters of the English alphabet if no letter can be repeated? 
• Problem 4: How many 5-digit telephone numbers can be constructed using the digits 0 to 9 if each number starts with 67 and no digit appears more than once?
• Problem 5: A coin is tossed 3 times and the outcomes are recorded. How many possible outcomes are there?
• Problem 6: Given 5 flags of different colours, how many different signals can be generated if each signal requires the use of 2 flags, one below the other?
• How many two digit numbers can be formed from 3/5 and 7 if no digit is repeated in any number?
• How many 2 digit numbers can be formed with the digits 3 5 6 7 8 if none of the digits is repeated in any of the numbers formed?
• How many 2 digit and 3 digit numbers can be formed using the digits 3 5 6 without repeating any digit?
• How many 3 digits number can be formed using the digits 1 3 5 7 9 where we are allowed to repeat the digits?

Answer: 125.

Method:

Here, Total number of digits = 5

Let 3-digit number be XYZ.

Now the number of digits available for X = 5,

As repetition is allowed,

So the number of digits available for Y and Z will also be 5 (each).

Thus, The total number of 3-digit numbers that can be formed = 5×5×5 = 125.

(ii) repetition of the digits is not allowed? 

Solution:

Answer: 60.

Method:

Here, Total number of digits = 5

Let 3-digit number be XYZ.

Now the number of digits available for X = 5,

As repetition is not allowed,

So the number of digits available for Y = 4 (As one digit has already been chosen at X),

Similarly, the number of digits available for Z = 3.

Thus, The total number of 3-digit numbers that can be formed = 5×4×3 = 60.

Problem 2: How many 3-digit even numbers can be formed from the digits 1, 2, 3, 4, 5, 6 if the digits can be repeated?

Solution:

Answer: 108.

Method:

Here, Total number of digits = 6

Let 3-digit number be XYZ.

Now, as the number should be even so the digits at unit place must be even, so number of digits available for Z = 3 (As 2,4,6 are even digits here),

As the repetition is allowed,

So the number of digits available for X = 6,

Similarly, the number of digits available for Y = 6.

Thus, The total number of 3-digit even numbers that can be formed = 6×6×3 = 108.

Problem 3: How many 4-letter code can be formed using the first 10 letters of the English alphabet if no letter can be repeated? 

Solution:

Answer: 5040

Method:

Here, Total number of letters = 10

Let the 4-letter code be 1234.

Now, the number of letters available for 1st place = 10,

As repetition is not allowed,

So the number of letters possible at 2nd place = 9 (As one letter has already been chosen at 1st place),

Similarly, the number of letters available for 3rd place = 8,

and the number of letters available for 4th place = 7.

Thus, The total number of 4-letter code that can be formed = 10×9×8×7 = 5040.

Problem 4: How many 5-digit telephone numbers can be constructed using the digits 0 to 9 if each number starts with 67 and no digit appears more than once?

Solution:

Answer: 336

Method:

Here, Total number of digits = 10 (from 0 to 9)

Let 5-digit number be ABCDE.

Now, As the number should start from  67 so the number of possible digits at A and B = 1 (each),

As repetition is not allowed,

So the number of digits available for C = 8 ( As 2 digits have already been chosen at A and B),

Similarly, the number of digits available for D = 7,

and the number of digits available for E = 6.

Thus, The total number of 5-digit telephone numbers that can be formed = 1×1×8×7×6 = 336.

Problem 5: A coin is tossed 3 times and the outcomes are recorded. How many possible outcomes are there?

Solution:

Answer: 8

Method:

We know that, the possible outcome after tossing a coin is either head or tail (2 outcomes),

Here, a coin is tossed 3 times and outcomes are recorded after each toss,

Thus, the total number of outcomes = 2×2×2 = 8.

Problem 6: Given 5 flags of different colours, how many different signals can be generated if each signal requires the use of 2 flags, one below the other?

Solution:

Answer: 20.

Method:

Here, Total number of flags = 5

As each signal requires 2 flag and signals should be different so repetition will not be allowed,

So, the number of flags possible for the upper place = 5,

and the number of flags possible for the lower place = 4.

Thus, the total number of different signals that can be generated = 5×4 = 20.

Answer : 64

Solution : One-digit numbers: <br> Clearly, there are four 1 -digit numbers. <br> Two-digit numbers: <br> We may fill the unit's place by any of the four given digits. <br> Thus, there are 4 ways to fill the unit's place. <br> The ten's place may now be filled by any of the remaining three digits. So, there are 3 ways to fill the ten's place. <br> Number of 2-digit numbers `=(4xx3)=12.` <br> Three-digit numbers: <br> Number of ways to fill the unit's, ten's and hundred's places are 4, 3 and 2 respectively. <br> Number of 3-digit numbers `=(4xx3xx2)=24.` <br> Four-digit numbers: <br> Number of ways to fill the unit's ten's, hundred's and thousand's places are 4, 3, 2 and 1 respectively. <br> Number of 4-digit numbers `=(4xx3xx2xx1)=24.` <br> Hence, the number of required numbers `=(4+12+24+24)=64.`

Detailed Solution ⇒ Number of possible two-digit numbers which can be formed by using the digits 3, 5 and 7 = 3 × 3. ∴ 9 possible two-digit numbers can be formed.

∴ Required number of numbers = (1 x 5 x 4) = 20. Was this answer helpful?

Solution : 357, 375, 537, 573, 735, 753. Therefore, '6' three-digit numbers can be formed.

Therefore, a total of 100 3 digit numbers can be formed using the digits 0, 1, 3, 5, 7 when repetition is allowed.

Solution:

A two-digit number has 2 digits, one at the units place and one at the tens place.

Let's form the two-digit numbers using the digits 3, 7, and 9 if the repetition of the digit is allowed.

Below are all the numbers formed using the digits 3, 7, 9 with 3 at tens place:

33, 37, 39

Below are all the numbers formed using the digits 3, 7, 9 with 7 at tens place:

73, 77, 79

Below are all the numbers formed using the digits 3, 7, 9 with 9 at tens place:

93, 97, 99

Therefore, the two-digit numbers formed by using the digits 3, 7, and 9 are 33, 37, 39, 73, 77, 79, 93, 97, and 99.

Summary:

All possible two-digit numbers formed by using the digits 3, 7, and 9 if repetition of the digit is allowed are 33, 37, 39, 73, 77, 79, 93, 97, and 99.

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Answer:

12 ways

Step-by-step explanation:

Using the permutation formula

P(n,r) = n! / (n-r)!

P(4,2) = 4! / (4-2)!

P(4,2) = 4! / 2!

P(4,2) = 4×3×2×1 / 2×1

P(4,2) = 4×3

P(4,2) = 12 ways