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JAMB Mathematics 2015 Paper

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Question : 12

Total: 61

The first and last term of a linear sequence (AP) are 6 and 10 respectively. If the sum of the sequence is 40. Find the number of terms

nth = 3
nth = 4
nth = 5
nth = 6

Solution:

nth term of a linear sequence (AP) = a+(n − 1)d

first term = 6, last term = 10 sum − 40

i.e. a = 6, l = 10, S = 40

S

_{n}

= n/2(2a + (n − 1)d or Sn = ÷2 (a + l)

S

_{n}

= n/2(a + l)

40 = n/2(6 + 10)

40 = 8n

8n = 40

8n = 40

n = 40/8

= 5

The number of terms = 5

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