(47 × 1 / 26) × 13 / 27 – (20 × 1 / 26) × 13 / 27 =
способы решения

(47*1/26)*13/27–(20*1/26)*13/27=13/27*(47*1/26-20*1/26)=13/27*(1/26*(47-20))=13/27*(1/26*27)=13/27*1/26*27=1/2