The sum of integers from 1 to 100 that are divisible by 2 or 5 is
=(2+4+6+⋯+100) +(5+10+15+⋯+100) −(10+20+30+⋯+100)=502(2+100)+202(5+100)−102(10+100)=50×(51)+10×(105)−10×(55)=2550+10×(105−55)=2550+500=3050
Sum of integers from 1 to 100 that are divisible by 2 is a, by 5 is b and by both 2 and 5 is c. Find the sum of integers which are divisible 2 or 5.