Exercise 21. a maths teacher bought 40 calculators at $8.20 each and a numberof other calculators costing $2.95 each. in all she spent $387.how many of the cheaper calculators did she buy?

20

Explanation:

40($8.20)+X($2.95)=$387.00

$328+$2.95X=$387.00

$2.95X=$59.00

X=$59.00/$2.95=20

X=20 calculators

neutrons are in the middle of the atom and the electrons, which are much smaller.

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.