Roblox takes 75% of each sale. This means the developer needs to make 400,000 in Robux sales before the developer accumulates 100,000 Robux for cash withdrawal.
If 100,000 Robux is sold for $1,000, and 100,000 Robux only nets the developer $350, then the double dip gives Roblox a net 91.25% of developer sales. This excludes any applicable taxes or app store fees.
They don't combine like that, because the 75% already takes into account the double dip.
User spends $100 USD to buy 10000 robux. User buys item for 10000 robux in a game. Developer of game gets 7000 robux (dip #1). Developer of game withdraws to USD. 100000 robux = $350 (dip #2) so developer gets $24.5 USD.
Overall 24.5/100 = 24.5%.
In reality the numbers don't always come exactly to this, because robux can cost different amounts to buy depending on the amount, and there are PayPal/wire transfer fees when withdrawing.
Roblox takes 75% of each sale. This means the developer needs to make 400,000 in Robux sales before the developer accumulates 100,000 Robux for cash withdrawal.
If 100,000 Robux is sold for $1,000, and 100,000 Robux only nets the developer $350, then the double dip gives Roblox a net 91.25% of developer sales. This excludes any applicable taxes or app store fees.