a = either 1,16,4,2,8; b is the same
but for a+b=10, a can only be 2 or 8
d=2 or 8 too, b=2 or 8 too
a=d so they are both 8 otherwise it couldn't add up to 23
a=8,c=5,d=8
23-8-8-5=2
b=2
8+2+5+8=23
这是一道算术题:a+b=10
a=d
ab=16
a+b+c+d=23
c=5,及:a=8,b=2,c=5.d=8.......