Nelson has half investments in stock paying a 6% dividend and the other half paying 9% intereat. if his annual interest is $600 how much does he have invested
now, how much is 6% of a? well, 6/100 * a or 0.06a how much is 9% of b? well 9/100 * b or 0.09b
so... both interest yielded $600 in a year thus, we can say that 0.06a + 0.09b = 600
well, Nelson put half in "a" and half in "b", that means, "a" and "b" are just two equal halves, thus whatever amount he put in "a", is the same exact amount he put in "b", thus a = b or b = a
so 0.06a + 0.09b = 600 is really 0.06a + 0.09a = 600 <-----
