1 million 1,000,000
Four-digit phone numbers were primarily used in the United States before the widespread adoption of area codes and seven-digit dialing. This system was prevalent from the early 20th century until the late 1950s, when the North American Numbering Plan was introduced, requiring the use of three-digit area codes and seven-digit local numbers. The transition to seven-digit dialing became standard as more telephone lines were added and the need for more numbers grew.
252
Seven of them.
3 digit numbers are lessthan 4 digit numbers
16, 25, 34, 43, 52, 61, 70 Seven of them.
To find the total number of seven-digit numbers that contain the number seven at least once, we can use the principle of complementary counting. There are a total of 9,999,999 seven-digit numbers in total. To find the number of seven-digit numbers that do not contain the number seven, we can count the number of choices for each digit (excluding seven), which is 9 choices for each digit. Therefore, there are 9^7 seven-digit numbers that do not contain the number seven. Subtracting this from the total number of seven-digit numbers gives us the number of seven-digit numbers that contain the number seven at least once.
You have seven different digits (symbols) to choose from, so you can form seven different one digit numbers and 7×7=72=49 different two digit numbers.
420 and 840
In the 1940s, phone numbers typically consisted of a three-digit area code followed by a seven-digit local number, such as "ABC-1234." This format differed from modern phone numbers, which generally have a three-digit area code followed by a seven-digit local number, such as "(123) 456-7890."
Seven of them.
252
That makes:* 8 options for the first digit * 8 options for second digit * 10 options for the third digit * ... etc. Just multiply all the numbers together.
9,000,0009,999,999 is the last 7 digit number1,000,000 is the first 7 digit numberwhen you subtract the first from the last and add one you get the above answer.
3 digit numbers are lessthan 4 digit numbers
Same as the odd numbers anywhere else, except the first digit is always "7"
you say one number first then the other one for example 789 you say seven eight and then nine
16, 25, 34, 43, 52, 61, 70 Seven of them.