I do this frequently in my forms, the thing to remember is that this solution will be erased by the use of the drop down, ok?

So, in B1, put the formula:

=IF(A1="", "", LOOKUP(A1, {"A","B","P"}, {"Apples","Bananas","Pineapples"}))

Now, as soon as A1 is filled in, B1 will automatically display the answer via this formula.

However, your Data Validation might still be available based on how you set it up. Regardless, if anyone ever uses the data validation drop down list, it will permanently enter a choice into that cell and the formula will be deleted. That may be just fine, it is in my forms since each form is "one use" only and the agents start with a fresh clean form each time with all formulas intact to start with.

Just my idea.