Question

If t11 =16 t21=29 find a+d

Answer 1

Answer:

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Step-by-step explanation:

t­11 = 16 and t21 = 29    [Given]

We know that,

tn =  a + (n – 1 )d

t11 = a + (11 – 1 )d

∴ 16 = a + 10d    ---------eq. no. 1

t21 = a + (21 – 1) d

∴ 29 = a + 20 d  --------eq. no. 2

Subtracting eq. 1 from eq. 2

29 = a + 20 d

16 = a + 10d    

13 = 0 + 10d

13 = 10d

13/10 = d

∴ d = 1.3

Substituting d = 1.3 in eq. no. 1

16 = a + 10d

16 = a + 10(1.3)

16 = a + 13

16 – 13 = a

∴  a = 3

a + d = 3 + 1.3

∴ a + d = 4.3

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