Question Number 116921 by Engr_Jidda last updated on 08/Oct/20
Answered by $@y@m last updated on 08/Oct/20
$${a}=\mathrm{2500},\:{d}=\mathrm{500} \\ $$$$\left(\mathrm{a}\right)\:\mathrm{S}_{\mathrm{18}} =\frac{\mathrm{18}}{\mathrm{2}}\left\{\mathrm{2}×\mathrm{2500}+\mathrm{17}×\mathrm{500}\right\} \\ $$$$=\mathrm{9}×\mathrm{13500}=\mathrm{1},\mathrm{21},\mathrm{500} \\ $$$$\left(\mathrm{b}\right)\:{t}_{\mathrm{20}} =\mathrm{2500}\:+\:\mathrm{20}×\mathrm{500}=\mathrm{12500} \\ $$
Commented by Engr_Jidda last updated on 08/Oct/20
$$\mathrm{thank}\:\mathrm{you}\:\mathrm{sir} \\ $$