In an examination 31 student passed chemistry 29 pass physics and 3 fail both. If 50 people sat for the exam, how many of them pass chem only

Answer 1

This can be easily solved with a Venn diagram.

Draw a rectangle to describe the total number of people.
Inside draw 2 intersecting circles and label them C and P
Enter x in the intersection of the two circles
In the C circle enter 31-x in the "chemistry only " part
In the P circle enter 29-x in the "physics only" part
Enter 3 outside the circles but inside the rectangle, now solve
31-x + x + 29-x + 3 = 50

then evaluate 31-x

Answer 2

x=13
then 31-(x)13=18