Let a_1=1 and define a_(n+1) to be the least integer greater than a_n which cannot be written as the sum of at most h>=2 addends among the terms a_1, a_2, ..., a_n. This defines the h-Stöhr sequence
R = speed in still water r + c = speed with current r - c = speed against current
3.5(r + c) = 70 r + c = 20 c = 20 - r
4(r + c) = distance from pier to pier 5(r - c) = distance from pier to pier 4(r + c) = 5(r - c) 4(r + 20 - r) = 5(r - 20 + r) 80 = 10r - 100 180 = 10r 18 = r The speed in still water is 18 km/hour
