Question

How many numbers between 100 and 1000
have the digit 7 exactly once?​

Answer 1

Numbers between 100 and 1000  have the digit 7 exactly once is 225.

Step-by-step explanation:

To find : How many numbers between 100 and 1000  have the digit 7 exactly once?​

Solution :

The numbers between 100 and 1000 having 7 as exactly one of their digits can be :

1) When the units place has 7 :

Tens place can have any one of the digits except 7.

So, it can be filled in 9 different ways.

The hundreds place can have any one of the digits except 0 and 7.

So, it can be filled in 8 different ways.

There are $9 \times 8 = 72$ such numbers.

 2) When the tens place has 7:

The units place can have any one of the digits except 7.

So, it can be filled in 9 different ways.

The hundreds place can have any one of the digits except 0 and 7.

So, it can be filled in 8 different ways.

There are $9 \times 8 = 72$ such numbers.

3)  When the hundreds place has 7 :

Units place can have any one of the digits except 7.

So, it can be filled in 9 different ways.

The tens place can have any one of the digits except 7.

So, it can be filled in 9 different ways.

There are $9 \times 9= 81$ such numbers.

The required number of numbers = 72 + 72 + 81 = 225.

Therefore, numbers between 100 and 1000  have the digit 7 exactly once is 225.

#Learn more

How many numbers between 100 and 1000  have the digit 7 exactly once?​

https://brainly.in/question/13210076

Answer 2

Answer:

225

Step-by-step explanation:

in ones place there is 8

in tens place there is 9

in ones place there is 8

in hundreds place there is 9

in tens place there is 9

in hundreds place there is 9

72+72+81=225