basically
monday $${\mathtt{0.5}}{\mathtt{\,\times\,}}{\mathtt{1.5}} = {\frac{{\mathtt{3}}}{{\mathtt{4}}}} = {\mathtt{0.75}}$$
then
tuesday $${\mathtt{0.75}}{\mathtt{\,\times\,}}{\mathtt{1.5}} = {\frac{{\mathtt{9}}}{{\mathtt{8}}}} = {\mathtt{1.125}}$$
and
wednesday $${\mathtt{1.125}}{\mathtt{\,\times\,}}{\mathtt{1.5}} = {\frac{{\mathtt{27}}}{{\mathtt{16}}}} = {\mathtt{1.687\: \!5}}$$
and so on by multiplying the result of the last sum by 1.5
then round the results as required to 1 decimal place
0.8 , 1.2 , 1.7 etc.