A three-person committee must be chosen from a group of 10 professors and 10 graduate students. If at least one of the people on the committee must be a professor, how many different groups of people could be chosen for the committee?
Choose the correct choice from the following:
A) A)70
B) B)1020
C) C)630
D) D)1,260
E) E)1,980
Total number of ways to select at least one professor = Number of ways to select 3 people from 10 students and 10 professors - Number of ways to select 3 people from 10 student (i.e. without including any professor)   = 20C3 - 10C3 = 1140 - 120= 
<gadget id="calculator">1140 - 120</gadget>
<output>1_020</output>
1020   ANSWER:1020
<result>B</result>
A three-person committee must be chosen from a group of 10 professors and 10 graduate students. If at least one of the people on the committee must be a professor, how many different groups of people could be chosen for the committee?