OOP versus functional design styles

An important part of my job is to work with programmers and help them to improve the way they write code. To do so, I try my best to come up with simple explanations for complex ideas. I have one such explanation for software design. Software design is, for me, the way we structure the code such that we optimize it for business purposes.

I like this definition because it's plain and short. But one thing bugged me after I started experimenting with functional constructs; that is, functional programming leads to code such as the following:

const Sums sumsWithFunctionalLoopsSimplified(const vector<int>& numbers){
    Sums theTotals(
        sum(filter(numbers, isEven)),
        sum(filter(numbers, isOdd)),
        sum(numbers)
    );
    return theTotals;
 }

Writing similar code in OOP style would most likely mean creating classes and using...