Seven times the number of quarters in a coin collection is the same as three times the number of quarters increased by 20. How many quarters in the collection

5

Explanation:

Let P be the number of quarters in a coin collection.

Seven times the number of quarters in a coin collection is expressed as;

7×P

= 7P... (1)

Also three times the number of quarters can be expressed as 3P. If this value is increased by 20, the resulting expression will be;

3P+20 (increment means addition)...(2)

If the two expression are the same then equation 1 = equation 2 i.e

7P = 3P + 20

7P-3P = 20

4P = 20

P = 20/4

P = 5

Therefore the number of quarters in the coin collection is 5

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form