## Elementary Algebra

Let o be the number of ones, f be the number of fives, and t be the number of twenty dollar bills. Thus, we obtain: $o + t + f = 24 \\ o + 20t + 5f = 150 \\ t = 2f$ We know from equation one that $o = 24 - t -f.$ We plug this into equation two to find: $24 + 19t + 4f = 150$ We plug in equation three to find: $38f + 4f = 126 \\ 42f = 126 \\ f =3$ Thus, we find: $t = 2f = 2(3) = 6$ Since there are 24 bills, we find: $o = 24 - 6 -3 = 15$