[x = amount earning 6% annually.]
(8000-x) = amount earning 15% annually
Then we set up our equation which is a sum of the 15% return and the 6% return and we let that sum equal our desired return on investment ($930). Then solve for x.
(8000-x)*.15 + x*.06 = 930
1200 - .15x + .06x = 930
.09x = 270
x = 3000.
Therefore, you should invest $3000 at 6% and $5000 at 15% to earn $930 annually.
The irrational number is 7.8. It is irrational because it does not terminate or repeat
If your question is to write it in scientific notation, it's 10^4 and the exponent is 4
