Imagine that you have four food dyes to test, A, B, C and D. Imagine that you going to investigate which food dye diffuses most quickly.
a. which variable will you change?
b. which variable will you measure? how will you do this?

explanation:

venn diagram is pictorial representation with of circles showing the relation between two finite sets or things. the intersection part of two circles conveys the relation present in between those sets or things.

here in the venn diagram of sand and salt two circles represent sand and salt. but the area falling under the intersection of these circle represents the mixture of sand and salt.

so, in a venn diagram the mixture will be placed in a middle that is in between the intersection of two circles.

it is the most commonly accepted one