Find the 21st term of the Arithmetic Progression (A.P.): -4, -1.5, 1, 3.5,...

  • A 43.5
  • B 46
  • C 48.5
  • D 51
waec 2017furthermathematics

The correct answer is B. 46

\(T_{n} = a + (n-1)d\)

\( d = T_{2} - T_{1} = T_{3} - T_{2} = -1.5 - (-4) = 2.5\)

\(T_{21} = -4 + (21 - 1) \times 2.5 = -4 + (20\times 2.5) \)

= \(-4 + 50 = 46\)

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