To find out how much the saleswoman should give her back, we have to find out first how much she spent. She bought apples for 5€, sugar for 3€ and carrots for 17€, so she spent 5€ + 3€ +17€ = <<5+3+17=25>>25€.
She pays 50€ and the saleswoman must keep 25€, so the seller must give her back 50€ - 25€ = <<50-25=25>>25€
#### 25