An infinite amount if you include decimals and negative numbers. 2.5+1.5=4
4, if you multiply them.
5
There are 15 of them.
2x2=4
Yes. The entire set of natural numbers is closed under addition (but not subtraction). So are the even numbers (but not the odd numbers), the multiples of 3, of 4, etc.
4, if you multiply them.
There are infinitely many answers and these depend on what is done with the two numbers: addition, multiplication, exponentiation and so forth.In each case, there are infinitely many answers. For example, with addition,67.2 + 67.267.1 + 67.367.0 + 67.4...0.1 + 134.30.0 + 134.4-0.1 + 134.5-0.2 + 134.6etc.Then you can add numbers to two decimal places, to 3 do, 4 dp, ... infinitely many dp.
4
5
There are 15 of them.
Yes - due to commutability, you can rearrange the numbers in any addition sum and the answer will still be the same.
1+2+3+53 is one quartet. There are an infinite number of possible quartets for addition alone. And then you can have sutractions. And then multiplications, and divisions.
This is not possible, 27 is an odd number, 4 odd numbers will always equal an even number.
143
2x2=4
20
Yes. The entire set of natural numbers is closed under addition (but not subtraction). So are the even numbers (but not the odd numbers), the multiples of 3, of 4, etc.