• Freeflows
  • Problems
    • Sign in
    Modulo Inverse Problem

    When working modulo $ m $, the notation $ a^{-1} $ is used to denote the residue $ b $ for which $ ab\equiv 1\pmod{m} $, if any exists. For how many integers $ a $ satisfying $ 0 \le a < 100 $ is it true that $ a(a-1)^{-1} \equiv 4a^{-1} \pmod{20} $?

    • 1
    • 2
    • 3
    • +
    • 4
    • 5
    • 6
    • -
    • 7
    • 8
    • 9
    • $\frac{a}{b}$
    • .
    • 0
    • =
    • %
    • $a^n$
    • $a^{\circ}$
    • $a_n$
    • $\sqrt{}$
    • $\sqrt[n]{}$
    • $\pi$
    • $\ln{}$
    • $\log$
    • $\theta$
    • $\sin{}$
    • $\cos{}$
    • $\tan{}$
    • $($
    • $)$
    • $[$
    • $]$
    • $\cap$
    • $\cup$
    • $,$
    • $\infty$

    Sign in to save your progress!