Sam has 18 coins in his pocket that are either quarters or nickels. the total value of these coins is $3.90. let q represent the number of quarters and n represent the number of nickels. the following system of equations represents this situation: q+n=18 0.25q+0.05n=3.90 how many quarters and nickels does sam have?

Q=18-n

0.25 (18-n) + 0.05n=3.90
 (4.5-0.25n) + 0.05n=
             4.5 - 0.30n= 3.90
                   - 0.30n= -0.60
                             n=2
                             q=16

the law of definite proportions states samples of a compound will always contain the same proportion of elements by mass. in other words, a given compound will always contain the same elements in the same proportions by mass.the law of multiple proportions states when two elements combine with each other to form more than one compound, then the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers.