How many one in 400 to 500?

Answer 1

Assuming you are asking how many times the digit 1 appears when writing the numbers 400 to 500:

It appears in the tens place once (41x where x is any digit 0-9) so there will be 10 occurrences of it here.

It appears in the ones place for every digit in the tens place (4x1) so there will be 10 occurrences of it here.

However, the number 411 has been counted twice, once as 41x and again as 4x1.

Thus the digit 1 will be written 10 + 10 - 1 = 19 times.

Answer 2

There are 200000 lots of 1/400 in 500.