Question

A number round off to 4000. The digit in the hundreds place is twice the digit in the tens place. The sum of the digits is 12. The numbers uses only two different digits. Find the number.

Answer 1

4*1000 + c*100 + b*10 + a*1


c < 5 so 0, 1, 2, 3 or 4
c = 2 b so c is even, 0, 2, or 4

4 + c + b + a = 12
so
c + b + a = 8

if c = 0 ,b = 0 because c=2b
4 0 0 4 does NOT add to 12.

if c = 2
4 2 1 mope, only two digits allowed

if c = 4
4 4 2 2
ah ha, 4422 seems to work