Mango Unit Rates

A store was selling 8 mangos for $10 at the farmers market. 
Keisha said, “That means we can write the ratio 10 : 8, or $1.25 per mango.”
Luis said, “I thought we had to write the ratio the other way, 8 : 10, or 0.8 mangos per dollar."

Who’s right?

Both Luis and Keisha are both mathematically correct.

Keisha's unit rate was the amount of money per mango, which was $1.25. She divided the $10 by the 8 mangos, so each mango costed the same amount of money, and got $1.25 per mango.

Luis's unit rate was amount of mango you can get per $1. He divided 8 mangoes by $10, so each dollar was worth the same amount of mango: 0.8 of a mango.