Question 515276
Let
Number = x
Half of the x = x/2
Other half = x/2

He had to divide a half of 'x' by 6 and other half by 4 and then add the two quantities

=(x/2/6)+(x/2/4)
=(x/2)*(1/6)+(x/2)*(1/4)
=x/12+x/8
Take LCM 
=(2x+3x)/24
=5x/24 (This the correct answer)



But



He divided the 'x' by 5 and got the answer which was 4 shorter of the correct answer
=x/5 (wrong answer short of 4)
if we add the 4 in above equation then correct answer and wrong answer will be sam
=(x/5)+4
So
5x/24=(x/5)+4
5x/24-(x/5)=4
Take LCM
(5*(5x)-(24*x))/120=4
(25x-24x)/120=4
x/120=4
Multiply by 120 both sides
120*x/120=4*120
x=480
Number is 480


Check
======
What he suppose to do
=(240/6)+(240/4)
=40+60
=100

What he actually did
=480/5
=96 (which is 4 shorter than the actual answer)