Question

43+50+57+...+743=?
:-) :-) :-) :-) :-) :-) :-)

Answer 1

43*{743-43)/7}=
43*100=4300
4300+7(1+2+...+100)=
4300+7*100*101/2=
4300+35350=39650

Answer 2

scadem din fiecare termen cate 43
obtinem sirul 0+7+14+...+700
dam factor comun 7, obtinem 7(0+1+2+...+100)
de mai sus deducem ca am avut 101 termeni din care l-am scazut pe 43

7(1+2+...+100)+101*43=$7( \frac{100*101}{2})+101*43=7*5050+101*43= 35350+4343=39693$