Book value of share after repurchase

When Market price>book value, book value reduce after repurchase. Can some one help me with the logic here?

  • Assets = 100
  • Liabilities = 60
  • Equity = 40
  • 5 shares outstanding
  • BV per share = 8
  • MV per share = 10

You buy back one share.

  • Assets = 90
  • Liabilities = 60
  • Equity = 30
  • 4 shares outstanding
  • BV per share = 7.5

Thanks a lot

You’re welcome.