20. Steven subtracts the units digit from the tens digit for each two-digit number. He then finds the sum of all his answers.
What is the value of Steven's sum?
A 30
B 45
C 55
D 90
E 100
20. B The sum of all the tens digits is $(1+2+3+4+5+6+7+8+9) \times 10$.
The sum of all the units digits is $(0+1+2+3+4+5+6+7+8+9) \times 9$. Therefore Steven's sum is $(1+2+3+4+5+6+7+8+9) \times 1=45$.