Step 1: Identifying the type of sentence.
We are given three simple sentences, and we need to combine them into a compound sentence. A compound sentence contains two independent clauses connected by a coordinating conjunction like "and," "but," "or."
Step 2: Analyzing the sentence.
- The first two sentences are stating that both mangoes are sweet.
- The third sentence adds a contrast by stating that only one of the mangoes is sweet.
To combine the sentences, we need to show the contrast in a single sentence.
Step 3: Combining the sentences.
We can use "but" to show the contrast. The sentence becomes:
This mango is sweet, but that mango is not; only one mango of them is sweet.
Final Answer: \[ \boxed{\text{This mango is sweet, but that mango is not; only one mango of them is sweet.}} \]