Question

find the greatest number of 7 digits which is exactly divisible by 12,15 & 21

Answer 1

Find the LCM of 12, 15 and 21. Multiply the LCM by a positive integer so large that you get the largest 7 digit number.
(The LCM is 420 and you multiply with 23809 to get 9999780 the largest 7 digit number exactly divisible by all the three numbers 12, 15 and 21)

Answer 2

For this, Find LCM of 12, 15 and 21
i.e. 420.
Now, since we want a 7 digit number, so, we must Multiply 420 with some number such that it becomes 7 digit..
To find by which number to Multiply, Divide 420 by largest 7 digit number, i.e. 9999999.
So, 9999999÷420 = 23809.5214

So let's try multiplying 23809 with 420,
23809×420 = 9,999,780 Answer!