The mid price is the current price half-way between the highest bid (buy) order and the lowest ask (sell) order on the open order book for a given token. It represents a "middle value" of a token's price at any given time, without assuming the viewer of the price is looking at it from any particular buy/sell bias.
10 XYZ * 2 USD = 20 USD
40 XYZ * 1 USD = 40 USD
50 XYZ * 0.5 USD = 25 USD
Totaling up to: 20+40+25 = 85 USD
We understand that you might have additional questions regarding this topic so you are welcome to contact us any time via the Xumm Support xApp in Xumm or you can simply scan this QR code with Xumm and be directed there automatically.