Find the sum of all even numbers between 20 and 200.

20+22+24+26+28+30+32+34+36+38+40+42+44+46+48+50+52+54+56+58+60+62+64+66+68+70+72+74+76+78+80+82+84+86+88+90+92+94+96+98+100+102+104+106+108+110+112+114+116+118+120+122+124+126+128+130+132+134+136+138+140+142+144+146+148+150+152+154+156+158+160+162+164+166+168+170+172+174+176+178+180+182+184+186+188+190+192+194+196+198+200=10010

200 - 20=180 all numbers 

180/2 +1=91 terms

(F+(F+(N-1) X D)) X 1/2 X N=

(20+(20+(91-1) X 2)) X 1/2 X 91=10,010