A collection of coins contains 15 pennies, 14 dimes and 6 quarters. What is the percentage of pennies in the collection?

42.9%

Explanation:

the total number of coins is 15+14+6 = 35

so to find the % of pennies, divide the number of pennies by the total number of coins and times it all by 100

15/35 x 100 = 42.9%

what are the choices?

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.