If quantity t varies inversely with a quantity r , Then mathematically t α 1/r, Introducing a constant, t = k/r . When t = 6 then r = 5, therefore, 6 = k/5 k = 6×5 k = 30 (Constant of variation) Which means the equation connecting t and r will be t = 30/r To find the value of t when r = 15, we use the equation of this variation such that, t = 30/15 t = 2