How many three-digit numbers are greater than 100 and increase by 198...
Solution:
Given that the three-digit number is greater than 100 and increases by 198 when the digits are reversed.
Let the number be of the form ABC, where A, B, and C are digits.
When the digits are reversed, the number becomes CBA.
Therefore, the number increases by (CBA - ABC) = (100C + 10B + A) - (100A + 10B + C) = 99C - 99A = 99(C - A).
We know that the number increases by 198, which is a multiple of 99.
Therefore, (C - A) must be either 2 or -2.
Case 1: (C - A) = 2
In this case, C can be any digit from 5 to 9, and A can be any digit from 0 to 4.
For each value of C, there is only one possible value of A that satisfies the condition.
Therefore, the total number of three-digit numbers in this case is 5.
Case 2: (C - A) = -2
In this case, A can be any digit from 5 to 9, and C can be any digit from 0 to 4.
For each value of A, there is only one possible value of C that satisfies the condition.
Therefore, the total number of three-digit numbers in this case is 5.
Hence, the total number of three-digit numbers that satisfy the condition is 5 + 5 = 10. However, we need to exclude the number 198, which is less than 100.
Therefore, the final answer is 10 - 1 = 9.
However, we need to consider the fact that the digits cannot be repeated.
Case 1: (C - A) = 2
In this case, there are 5 possible values of C and 5 possible values of A that satisfy the condition.
Therefore, the total number of three-digit numbers in this case is 5 x 5 = 25.
However, we need to exclude the cases where the digits are repeated.
When C = 9, A can only be 7.
When C = 8, A can only be 6 or 8.
When C = 7, A can only be 5 or 7.
Therefore, the total number of three-digit numbers in this case is 25 - 4 = 21.
Case 2: (C - A) = -2
In this case, there are 5 possible values of A and 5 possible values of C that satisfy the condition.
Therefore, the total number of three-digit numbers in this case is 5 x 5 = 25.
However, we need to exclude the cases where the digits are repeated.
When A = 9, C can only be 1.
When A = 8, C can only be 0 or 2.
When A = 7, C can only be 3 or 5.
When A = 6, C can only be 4 or 6.
Therefore, the total number of three-digit numbers in this case is 25 - 6 = 19.
Hence, the total number of three-digit numbers that satisfy the condition and do not have repeated digits is 21 + 19 = 40.
However, we need to exclude the number 198
How many three-digit numbers are greater than 100 and increase by 198...
Let the numbers be of the form 100a+10b+c, where a, b, and c represent single digits.
Then (100c + 10b + a) - (100a + 10b + c) = 198
99c - 99a = 198
c - a = 2.
Now, a can take the values 1-7. a cannot be zero as the initial number has 3 digits and cannot be 8 or 9 as then c would not be a singledigit number.
Thus, there can be 7 cases.
B can take the value of any digit from 0-9, as it does not affect the answer. Hence, the total cases will be 7 × 10 = 70.