52 years old
39
Any two digit number in which: (a) the units digit is not 0, and (b) the two digits are different will form a new 2-digit number when the digits are interchanged.
There are four pair of mirror primes.
472.
The answer is 418. You are copying a MathCounts problem.
There are three. If not, the final zero should not be present.
one
4 on each foot (16)
One way of doing this is through trial and error. Choose a random number where the digits add up to 14. There isn't that many, the numbers are:59 and 68. 5+9= 14. However 95 -59 is 36, twice as much as 18. 6+8=14. And 86-68 is 18. So the number is 68.
At most 1.
Canadian postal codes, which are actually integrated with British postal codes, generally contain six digits (the digits can be numbers or letters depending on their position) with a space half way in between, e.g. T6E 2T2 is Edmonton, Alberta.
There are three sig fig.(The final zero is significant as it is present when it would not normally be written.)