The number of terms between 11 and 200 which are divisible by 7 but not by 3 is -

Multiple of 7 between 11 and 200 are 14, 21, 28, 35, 42,....., 189, 196
T_m = 196 ⇒ 14 + (m - 1) × 7 = 196
⇒ (m - 1) × 7 = 182
⇒ (m - 1) = 26
⇒ m = 27.
Multiples of 7 and 3 both i.e. that of 21 are 21, 42, 63,......., 189
T_n = 189
⇒ 21 + (n - 1) × 21 = 189
⇒ (n - 1) × 21 = 168
⇒ (n - 1) = 8
⇒ n = 9.
Required number of terms = (27 - 9) = 18
Answer : 18