context: ###List of Questions
  (1) Two letters picked without replacement from {d: 2, i: 1}. What is prob of picking 2 d?
  (2) Solve -11 = -2*j + 3*i, 4*i = 4*j + i - 7 for j.
  (3) In base 3, what is 10010 + -201?
  (4) How many millilitres are there in 49.51404l?
  (5) Let r(n) = n**3 + 23*n**2 - 3*n - 49. What is the units digit of r(-23)?
q_1: (1) Two letters picked without replacement from {d: 2, i: 1}. What is prob of picking 2 d?
q_2: (2) Solve -11 = -2*j + 3*i, 4*i = 4*j + i - 7 for j.
q_3: (3) In base 3, what is 10010 + -201?
q_4: (4) How many millilitres are there in 49.51404l?
q_5: (5) Let r(n) = n**3 + 23*n**2 - 3*n - 49. What is the units digit of r(-23)?