The number of common terms in the two sequences $18, 24, 30, 36, \ldots, 606$ and $14, 24, 34, 44, \ldots, 604$ is:
Answer and solution
Correct answer: C
Solution
First common term = 24; LCM(6,10) = 30. Common terms: 24, 54, 84, ..., up to min(606, last term of 2nd seq). Last term of 2nd seq: $14+10k\le606\Rightarrow k\le59.2$. Last: 604. Common terms up to 604: $\lfloor(604-24)/30\rfloor+1=20$