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16. If a committee of 3 is to be selected from a group of 15 students and 6 teachers, then the number of different possible committees that have at least 1 teacher is A. 630 B. 875 C. 1 085 D. 1 260 17. The middle term in the expansion of (a2 + a3)6, written in ascending powers of a, is A. 15:;16 3. 15a55 C. 20:15 D. 204:!15 18. There are 6 terms in the expansion of (x + 4)\". The value of n is i and the value of the constant term in the expansion is ii The statement above ls completed by the information in row . 3 1 8 . . . . . 19. In the expansuon of (x + E written In descending powers of x, the snxth term IS 28 7 A B x 4:: 1 7 C. 642:6 D\" 162:6 20. A circle is drawn with 6 points on its circumference, as shown in the diagram below. A student creates polygons with 3 or more sides by connecting the points with straight lines. The number of polygons that can be created that must have at most 4 sides is A. 15 B. 20 C. 22 D. 35