context: ###List of Questions
  (1) Calculate the lowest common multiple of (21*-1 + -1)/(-2) and 6.
  (2) What is prob of sequence kisi when four letters picked without replacement from fsfkifefs?
  (3) What is (-5)/2*(-136)/170?
  (4) Suppose 36 = f + 3*f. Let s = -5 + f. Solve -3*p - 4*r = 0, -4 = -0*p - 2*p - s*r for p.
  (5) How many seconds are there in seven thirds of a minute?
q_1: (1) Calculate the lowest common multiple of (21*-1 + -1)/(-2) and 6.
q_2: (2) What is prob of sequence kisi when four letters picked without replacement from fsfkifefs?
q_3: (3) What is (-5)/2*(-136)/170?
q_4: (4) Suppose 36 = f + 3*f. Let s = -5 + f. Solve -3*p - 4*r = 0, -4 = -0*p - 2*p - s*r for p.
q_5: (5) How many seconds are there in seven thirds of a minute?