70 trees were planted by Parth and 90 trees were planted by Pradnya on the occasion of Tree Plantation Week. Out of these; 25 trees were planted by both of them together. How many trees were planted by Parth or Pradnya ?

Let A be the set of tress planted by Parth and B be the set of trees planted by Pradnya.

So, n (A) = 70; n (B) = 90; $n(A\cap B)=25$

Now,

$n\left(A\right)+n\left(B\right)=n(A\cup B)+n(A\cap B)$

$n(A\cup B)=70+90-25$

݅݅݅$n(A\cup B)=135$

Hence, the number of trees planted by Parth or Pradnya is 135.