let the percentage of the weight of tin in the alloy be
a%.
Percentage of the weight of lead in alloy = 100 - a %
a/100 x 1 x 7.3 + (100 - a)(1/100)(1)(11.3) = 8.5
7.3/100 (a) + (1-a/100)(11.3) = 8.5
0.073 a + 11.3 - 0.113a = 8.5
0.04 a = 2.8
a = 70
Percentage of the weight of tin = 70%
Percentage of lead in alloy = 30%
Then, check your ans back into the eqn.
7.3 x 0.7 + 11.3 x 0.3 = 8.5 (proven)
