Find the common ratio of the sequence. -172,-86,-43,-21.5

The common ratio is 1/2.

Step-by-step explanation:

Each term is half as much as the last one.  This means that to find the next term, you are multiplying the last term by 1/2.  The common ratio of a geometric sequence is the number that you multiply by to get the next term in the sequence, so it is 1/2 in this case.

Regular selling price (price before discount) 100%.

Price after trade discount of 15% is 85% of regular selling price..

Price after trade discount reduced to 10% is 90% of regular selling price.

By reducing the trade discount from 15% to 10% meant increasing the selling price by 5% of the selling price before applying the trade discount.