It sounds alright, but I would suggest changing the structure of the sentence slightly. Maybe to: "His strong foundation and passion for math have given him the ability to think outside the box."

I agree with John, his sentence is perfect. To give you another choice, you could have; "His combined passion and a strong foundation in math have given him the ability to think outside the box"

Or you could say, "A combination of his strong foundation and great passion for maths has given him the ability to think out of the box."