It's 40% off if you spend $50. You spend $50, you save $20.
You save $30 if you spend $100.
Therefore, you're better off just staying as close to $50 as possible, so you can get the biggest discount (40%). Once you get close to $100, you're better off getting over the $100 hump, so that you can get a 30% discount.
Spend $30 and you save $10 (33% discount).
Code is A123
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