In an AP, the ratio of the 2nd term to the 7th term is 1/3. If the 5th term is 11, what is the 15th term? A. 28 B. 31 C. 33 D. 36
Answers
Answered by
8
Answer:a+d/a+6d=1/3
=3a+3d=a+6d
=2a=3d
=2a-3d=0......›1
a+4d=11........›2
2(11-4d)-3d=0
22-8d-3d=0
22-11d=0
d=2
a+4d=11
a=11-8
a=3
a15=3+(14)×2
=3+28=31
Step-by-step explanation:
Hope u can understand it...
Answered by
3
Let the first term be ‘a’ and common difference be ‘d’
From first relation
(a+d)/(a+6d) = 1/3
Therefore by cross multiplying
3a+3d = a+6d
2a - 3d = 0 ......eq(1)
a+4d = 11 ...... eq(2)
Multiplying eq(2) by 2 and subtracting eq(1) from eq(2).
11d = 22
Therefore d = 2
And substituting d in eq(1)
a = 3
Now 15th term will a+ (15-1)d
ie 3 + 14(2) = 31
From first relation
(a+d)/(a+6d) = 1/3
Therefore by cross multiplying
3a+3d = a+6d
2a - 3d = 0 ......eq(1)
a+4d = 11 ...... eq(2)
Multiplying eq(2) by 2 and subtracting eq(1) from eq(2).
11d = 22
Therefore d = 2
And substituting d in eq(1)
a = 3
Now 15th term will a+ (15-1)d
ie 3 + 14(2) = 31
Similar questions