If rounded to the nearest 100, then any number between 150 and 250.
If rounded to the nearest 10, any between 195 and 205.
[For rounding fives, I round so that the last digit after rounding is even. This avoids the bias introduced when you always round up 5s or always round down 5s.]
Chat with our AI personalities
199 If it's 200 rounded to nearest ten, then the number must be between 195 and 205. Only 199 has the correct digit sum.
200*200=400 200+200=400
The digit in the tens position is 7, so the number is rounded up to 200.
Three numbers that fit these criteria are:108, 144, and 180.
Any prime numbers of about 66 or 67 digits will do.