Step 1. As a reference to solve this problem, we will call the original quantity ''x''
Step 2. The first discount applied is 70% --> to calculate this discount we multiply our original quantity by 0.7:
Step 3. Now we apply the second discount in the series of discounts which is a 10% discount. We need to multiply the previous result by 0.1:
Step 4. The last of the discounts is a 20% discount over the already discounted amount, so again we multiply the previous result but this time for 0.2 to find the 20% discount:
Step 5. Add all of the discounts:
The result is:
The equivalent discount is 0.784 of the original amount ''x''.
We can multiply this decimal number by 100 to find the equivalent percent discount:
The equivalent discount is 78.4%
Answer: 78.4%