the answer for that is 18 1+8=9 18/2=9
-109
1
Four. (100 x 10 = 1,000)
If you mean, "What is the largest number of digits possible in the product of two 2-digit numbers" then 99 * 99 = 9801, or 4 digits. Anything down to 59 * 17 = 1003 will have 4 digits.
19
It can have up to 5 digits.
Six.
81
You had me until "product." The product of 4 digits can't be prime.
362x(3x6)
-109
1
121
The number is 83.
-10
804
2