In Z₇, what is [3] × [5]?

Modulo Arithmetic & Congruence · Question 91 of 97

Question 91

MediumOriginal question

In $\mathbb{Z}_7$ , what is $[3] \times [5]$ ?

[15]

Correct answerYour answer

[1]

Correct answerYour answer

[8]

Correct answerYour answer

[2]

Correct answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer B

Correct answer: B

Multiply the representatives: $3 \times 5 = 15$ .
$15 = 7 \times 2 + 1$ , so $[3] \times [5] = [1]$ : 5 is the inverse of 3 modulo 7.

Worth noting

$[8]$ adds the representatives instead of multiplying them.

Ten questions from Modulo Arithmetic & Congruence, at your own pace.

Ten questions from Modulo Arithmetic & Congruence, at your own pace.