The sum of 2 digit numbers that are divisible by either 5 or 7 is

N.o of two digit numbers divisible by 5 = 10 , 15 ,20......95

N.o of two digit numbers divisible by 7=14 , 21 , 28.....98\

N.o of two digit numbers divisible by 35= 35, 70

Using $$S_{n\ }=\ \frac{n}{2}\left(2a+\left(n-1\right)d\right)$$

We can find out that the sum numbers divisible by 5 is 945

And sum of numbers divisible by 7 is 728

We need to subtract the numbers divisible by both 5 and 7 which is equal to 35+70=105

So total = 945+728-105= 1568