Substruct actually makes multiply

[w01fgang]

There is a typo in calculator.subtract

app.get('/', function (req, res) {
    var a = parseInt(req.query.a) || 1;
    var b = parseInt(req.query.b) || 1;
    var result = a * b;

    console.log('Subtract: a(%d) - b(%d) = %d', a, b, result);

    res.json({ result: result, a: a, b: b, operation: '-' });
})