Question

Its original quantity is 10 in the new quantity is 3 what is the percent decrease

Answer 1

This is markdown, thus once again, two equations. 
Markdown=Original-New
and
Markdown%=Markdown Amount/Original*100

Markdown=10-3
Markdown=7

Markdown%= 7/10*100
=0.7*100
=70

Thus, the percent decrease/Markdown is 70%.