Ajacket was $50 and is now on sale for $35.what is the percent change in the cost

Ok, it's all pretty much like the "$50 coat is on sale for $35".

If the regular price of the coat is $50 and now it is on sale for $35, then it will cost you $15 less, like this:
$50 - $35 = $15

You could also say the coat was discounted by $15, or the coat was reduced by $15, or you'll save $15 if you buy that coat ($50 - $15 = 35).

You could also put it in terms of percentages. If the discount is $15, you can figure that $15 is what percent of the regular price, like this:
$15 = X% of $50
$15 = X% x $50 (divide both sides by 50 to isolate X)
15/50 = X%
.30 = X% (multiply by 100 to convert to a non-decimal)
30% = X

So, you can say all of the following and they all mean the same thing:
1. the $50 coat is on sale for $35
2. the $50 coat is discounted by $15
3. the $50 coat is reduced by $15
4. you'll save $15 if you buy this coat
5. the $50 coat is on sale for 30% off
6. the $50 coat is discounted by 30%
7. you'll save 30% if you buy this coat
8. 30% savings!
9. Save 30%!