Let x be the original price of the object.
After the 40% discount, the price of the object now becomes;
x-0.4x=0.6x
0.6x is our new price after the first discount.
Now if we want to find the price after the second discount, (5%)
That would come off to be;
0.6x-0.6(0.05)x=0.6x-0.03x=0.57x
Our last price is 0.57x
If you notice, there was a 43% discount in total, as it goes to 57% of its original price.
This is very non intuitive for some people, as they may think there will be a 45% discount.