Division operation in `u128` results false value

Question

In my node, Balance type is u128. I have following variable

let per_block = 100_000_000_000_000_000_u128;
let total = 50_000_000_000_000_000_000_000_u128;
let ratio = per_block.checked_div(total);

assert!(ratio.is_some());
let user_a = 10_000_000_000_000_000_000_000_u128 * ratio;

But ratio is 0 even in above case. How do I perform such calculation to get user_a finally?

Playground: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=3d556bfb809632b885bf008680dfec8e

Answer 1

Check out the per_things.

You could use Perquintill here:

use sp_runtime::Perquintill;

let ratio = Perquintill::from_rational(per_block, total);
let user_a = 10_000_000_000_000_000_000_000_u128 * ratio;