Its very simple middle element is the sum of the corner elements in the triangle i.e. 50+30+10 =90 On the similar line missing element is 30 (90 - 40 - 20).
Sum if triangle is 90 so answer is 30.
Find the missing number in the image below.
Find the missing number.
Find the missing number. ?, 12, 55; 9, 7, 4; 61, 6, 31