Which of these describes f : N → N, f(n) = 2n?

Relations & Functions · Question 86 of 125

Question 86

MediumOriginal question

Which of these describes $f : \mathbb{N} \to \mathbb{N}$ , $f(n) = 2n$ ?

One-one but not ontoCorrect answerYour answerOne-one and ontoCorrect answerYour answerNeither one-one nor ontoCorrect answerYour answerOnto but not one-oneCorrect answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer A

Correct answer: A

$2a = 2b$ gives $a = b$ : one-one.
No natural number maps to 3, an odd number: not onto.

Worth noting

On $\mathbb{N}$ , doubling reaches only the even numbers.

Concept: Classifying a function
Typical timeTypical: 90 s
Your timeYours: —

The rule this testsOne-one functions

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Which of these describes f:N→Nf : \mathbb{N} \to \mathbb{N}f:N→N, f(n)=2nf(n) = 2nf(n)=2n?

Explanation

Which of these describes $f : \mathbb{N} \to \mathbb{N}$ , $f(n) = 2n$ ?