Do you need to declare data types in a class, after an interface?

Question

JavaScript

The Calculator class is implemented from ICalculator, where all the methods and their types are described, is it worth doing it again for class method parameters? If I remove it, then any type can be passed to the method. Please tell me how to write correctly, just started learning TypeScript

interface ICalculator {
    add(num: number): number;
    subtract(num: number): number;
    multiply(num: number): number;
    divide(num: number): number;
    print(): void;
}

class Calculator implements ICalculator {
    protected _res: number = 0;

    add(num:number) {
        return this._res = num + this._res;
    }

    subtract(num:number) {
        return this._res = this._res - num;
    }

    multiply(num:number) {
        return this._res = num * this._res;
    }

    divide(num:number) {
        return this._res = this._res / num ;
    }

    print():void {
        console.log(`Currently value: ${this._res}`);
    }
}
let myCalc = new Calculator();

myCalc.add(260);myCalc.subtract(12);
myCalc.multiply(12);myCalc.divide(2);
myCalc.print();