When test instructions say to Answer the multiple choice questions and fill in the blanks if known Does it mean to fill in the blanks only if known but answer all questions?

A test instruction that says, "Answer the multiple choice questions and fill in the blanks if known" could be very confusing to students (and students should ask for clarification before continuing the test).

It should be written more clearly as, "Answer the multiple choice questions and fill in the blanks" because most often you are expected to answer all questions on a test.

NOTE: If you ever see this on a standardized test, ASK before you start that section.