What is the least number of 4 digits which is divided by 12 ,15,20 and 35?
explain how you got the answer

Here, First of all, you need to calculate the LCM of 12, 15, 20 & 35
LCM of 12, 15, 20 & 35 is 420

Now, We know, smallest 4-digit number is 1000, 
Divide, 420 from 1000, It cuts on 840 (with quotient 2), 

So, we need next term, in order to know, just add another 420 to 840, which is:
840 + 420 = 1260

In short, Your Answer would be 1260

Hope this helps!

Get the primes for each number

12 = 2*2*3
15 = 3*5
20 = 2*2*5
35 = 5*7

So 2*2*3*5*7 = 420 , but we want the least 4-digit number =>
420*3 = 1260

The searched number is 1260