Answer:
a) 22583
b) 37345
Explanation:
Divisibility by 11
Rule: A number passes the test for 11 if the difference of the sums of alternating digits is divisible by 11.
For example, the number 14982 is divisible by 11. Sum the digits
1+9+2=12
4+8=12
Subtract them: 12-12=0. Since 0 is divisible by 11, then the number also is.
The number 745102 is not divisible by 11:
7+5+0=12
4+1+2=7
12-7=5. 5 is not divisible by 11.
a) 2_583. Let's call X to the unknown digit 2X583
2+5+3=10
X+8 should be 10 or 21, so 10-10=0 or 21-10=11 are divisible by 11, but X cannot be greater than 9, thus
X+8=10 => X=2. The number is 22583
b) 37X45
4+7=11
3+X+5 should be 11 or 21. Again, X must be less than 10, thus
3+X+5=11 => X=3. The number is 37345