Game math for scoring?

I'm not a game designer or developer so this question may be too basic.

I have a matching exercise for training and I'd like to take 3 factors into consideration and give a game-like score.
1. accuracy (100 if no mistake made)
2. time to complete (the shorter the higher game score)
3. extra steps in order to complete (-)

I also would like to have weight 50%, 30%, 20% for the 3 factors.

My goal is make the game score more varied and bigger number than 100 (like 10350 for high score). It seems the time to complete may be the key to make it varied.

What is the math to get a smaller number to become bigger? For example 40 second would generate a way bigger number than 120 second as an example.

Thanks for any suggestions.