Răspuns:
(1*1+1*2+1*3+1*4...+1*27+1*28+20):17
=1(1+2+3+4+...+27+28+20):17
=1(28*29:3+20):17
=1 (406+20):17
=1*426:17
=426:17
=25 rest 1
Sper ca te am ajutat :)
