Year	Number
1961	29.46272371903869
1962	30.285090379716124
1963	30.0442306069047
1964	30.5341370155783
1965	31.277196341906304
1966	32.216241055602964
1967	33.286038870817464
1968	33.43600628676054
1969	35.26816951613968
1970	35.87520233085141
1971	36.85965265880614
1972	42.26745217031505