First we will find the LCM of 12,15 and 36
By prime Factorisation,
12=2*2*3
15=5*3
36=2*2*3*3
Now, LCM= 22*32*5
We will find that the LCM is 180
Now, Largest 5 digit number= 99999
Dividing this number by LCM, we get,
99999/180=555.5
Now we will multiply 180 by 555
We will get 99900
We will check now and observe,
99900/12=8325
99900/15=6660
99900/36=2775
Hence 99900 is the greatest 5 digit number divisible by 12,15 and 36.
Hope this helps :)