Question
Question: The number of common terms to the two A.P's 17 + 21 + 25 + …..+ 417 and16 + 21 + 26 + …..+ 466 is...
The number of common terms to the two A.P's
17 + 21 + 25 + …..+ 417 and16 + 21 + 26 + …..+ 466 is
A
20
B
19
C
21
D
18
Answer
20
Explanation
Solution
d1 = 4, d2 = 5, first common term = 21
A.P. of common terms is
21 + 41 + 61 + …….
Let no. of common term is 'n'
then Tn = 417 = a+ (n –1) d
417 = 21 + (n –1) 20
20396+ 1 = n
n = 19.8 + 1
n = 20.8 Ï N
so number of common terms = 20