Question

what is the greatest number of four digits which is exactly divisible by 40 48 and 60

Answer 1

Greatest 4 digit number is 9999 but it is not exactly divisible by all the three numbers so, let's find the prime factorization of all these three:
40=2³×5
48=2³×3
60=2²×3×5
LCM(40,48,60)=120
Greatest number divisible by 120=9999-remainder(9999/120)

9999/120 gives remainder 39

Therefore number is 9999–39=9960