Which of the following pairs represent the same rational number?
−1620 and 20−25
−1620 and 20−25
⇒ consider the fraction −1620=−4×44×5=−45
similarly 20−25=4×5−5×5=−45
so we see that −1620 and 2025 basically represent the same rational number −45.
Hence, the answer is −45.