If a convex lens of focal length $80 \, cm$ and a concave lens of focal length $50 \, cm$ are combined together, what will be their resulting power?

  • A
    $+ 6.5 \, D$
  • B
    $-6.5 \, D$
  • C
    $+ 7.5 \, D$
  • D
    $-0.75 \, D$

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