Mary is younger than sue but jack Mary. this a simple sentence?

This sentence is not grammatically correct and is missing information to be considered a simple sentence. Here's why:

* Missing Verb: The sentence needs a verb to indicate what Mary does in relation to Jack. For example, "Mary is younger than Sue but is older than Jack."

* Unclear Relationship: The phrase "but jack Mary" doesn't make sense grammatically. It needs to be structured with a verb and a clear comparison.

To fix it, we need to know what the relationship between Mary and Jack is. Here are some possibilities:

* "Mary is younger than Sue but is older than Jack."

* "Mary is younger than Sue but is taller than Jack."

* "Mary is younger than Sue but is closer to Jack."

Once you provide the missing information, we can create a grammatically correct and understandable simple sentence.