Question

The shop declare a discount of 20% and later a discount of 15% after

Answer 1

In order to calculate the equivalent discount, consider the principle number is 100, 
Then, 100 - 100 * 0.20 = 100 - 20 = 80
Now, 80 - 80 * 0.15 = 80 - 12 = 68

So, Total discount would be: 100 - 68 = 32%

Hope this helps!