Let * be a binary operation on N given by a*b = LCM (a,b) for all $a,b \in N$. Find $5*7$.
Hint: To solve this question we have to understand that * is a binary operation means it will tell about what operation has to be done as like here we have to find LCM. Here 5*7 is given means we have to find LCM of 5 and 7.
Complete step-by-step answer: Here we have to find 5*7 Here * is a binary operation where it is given that a*b = LCM of a and b so We have to find LCM of 5 and 7. Hence LCM of 5 and 7 is $ \Rightarrow 5 \times 7 = 35$ Hence 5*7 is equal to 35.
Note: Whenever we get this type of question the key concept of solving is we have to understand the question that we have to replace * with what mathematical operation. And then do that mathematical operation to get an answer.