WBJEE 2019 Math Solved Paper

(B)
(3

1

8

+5

1

4

)84 = (5

1

4

+3

1

8

)84
Now Tn = 84Cn (5

84–n

4

)(3n∕8)
If Tn = rational ⇒ n is multiple of 8
⇒ n = 0, 8, 16,...... 80
⇒ n can take 11 terms ⇒ number of rational terms = 11
⇒ number of irrational terms = 85 – 11 = 74