WORCESTER POLYTECHNIC INSTITUTE
TWENTY-FIRST ANNUAL INVITATIONAL MATH MEET
OCTOBER 21, 2008
INDIVIDUAL EXAM QUESTION SHEET WITH ANSWERS
1. Consider the conic x2/9 +y2/16 = 1 and the line 3y – 4x = 12. At what points, if any, do they meet?
Ans: (-3,0 and (0,4) 1 point
2. A Double Mersenne Number, Dn, is of the form 4n – 1 where n is a positive integer. What is the binary form (base 2) for such a number?
Ans: 2n 1’s 1 point
3. The symbol 25b represents a 2 digit number to the base b. If the number 52b is twice 25b then what is the value of b?
Ans: b = 8 1 point
4. What is the number of digits in the number 212*58 ?
Ans: 10 1 point
5. A parabola is known to have its vertex at (2, 5) and its focus 2 units to the left of the vertex. What is its equation?
Ans: x-2 = -1/(4*2) (y-5)2 2 points
6. Two concentric circles are formed. What must be the ratio of the larger to smaller radii so that the area in between them is 84% of the area of the larger circle?
Ans: 2.5 : 1 ratio 2 points
7. Express as single complex number: 1 + i + i2 + i3 + . . . + i100 where i2 = - 1
Ans: 1 2 points
8. How many different 5 digit numbers can be constructed using the digits 1,1,1,4,7?
Ans: 20 2 points
9. The parabola y = ax2 + bx + c has vertex (p,p) and y intercept at (0, -p) where p ≠ 0. What must the value of b equal in order for this to happen?
Ans: b = 4 3 points
10. A fair six-sided die is tossed three times and the resulting sequence of numbers is recorded. What is the probability of the event E that either all of the numbers are equal or none of them is a 4?
Ans: p(E) = 7/12 3 points
11. Consider the solutions to the equation 3x2 – 4x + k = 0. The value of k for which the
product of the roots is a maximum is what?
Ans: k = 4/3 3 points