Question

If 20th term of an A.P is 99 and 3rd term is 14.Find the first and 4th term of it.

Answer 1

a20= a + (20-1)d
99 = a+ 19d. ...i

a3 = a +(3-1)d
14 = a+2d. ... ii

on subtracting ii from i
17d = 85
d =5

from eq ii
14 =a + 2*5
14 = a +10
a = 4

a4 = a +3d
= 4 + 3*5
= 4+15
= 19

Answer 2

a20= a + (20-1)d
99 = a+ 19d. ...i

a3 = a +(3-1)d
14 = a+2d. ... ii

on subtracting ii from i
17d = 85
d =5

from eq ii
14 =a + 2*5
14 = a +10
a = 4

a4 = a +3d
= 4 + 3*5
= 4+15
= 19


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