Of 60 children, 30 are happy, 10 are sad, and 20 are neither happy nor sad. There are 18 boys and 42 girls. If there are 6 happy boys and 4 sad girls, how many boys are neither happy nor sad? Choose one.
A) 2 B) 4 C) 6 D) 8 E) 10
Venn diagrams are useful for multiple values of a single variable e.g. State of mind - happy/sad/neither. When you have two or more variables such as here where you have gender - boy/girl too, it becomes unwieldy. In this case, either use the table or logic.   Table method is shown above; here is how you will use logic:   There are 6 happy boys.   There are 4 sad girls but total 10 sad children. So rest 6 sad children must be sad boys.   We have 6 happy boys and 6 sad boys. Total we have 18 boys. So  18 - 6 - 6= 
<gadget id="calculator"> 18 - 6 - 6</gadget>
<output>6</output>
6 boys must be neither happy nor sad.   Answer (6)
<result>C</result>
Of 60 children, 30 are happy, 10 are sad, and 20 are neither happy nor sad. There are 18 boys and 42 girls. If there are 6 happy boys and 4 sad girls, how many boys are neither happy nor sad?