What is the area between two concentric circles of diameters 26cm and 20cm?
 

  • A 100\(\pi\)
  • B 169\(\pi\)
  • C 69\(\pi\)
  • D 9\(\pi\)
  • E 269\(\pi\)
jamb 1981mathematics

The correct answer is C. 69\(\pi\)

The area between two concentric circles is the difference between the areas of the two circles. 

The radius of the larger circle is half its diameter, or 26cm / 2 = 13cm. 

The radius of the smaller circle is half its diameter, or 20cm / 2 = 10cm. 

The area of the larger circle is π * (13cm)^2 = 169π cm^2. 

The area of the smaller circle is π * (10cm)^2 = 100π cm^2. 

The area between the two circles is 169π cm^2 - 100π cm^2 = 69π cm^2.

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