Final answer:
The eldest son invested $80,000 in bonds.
Step-by-step explanation:
To solve this problem, we need to set up an equation using the information provided. Let x be the amount of money invested in bonds. The interest earned from the bonds can be calculated as 0.04x. The interest earned from the stocks can be calculated as 0.09(100,000 - x). The sum of these two interest amounts should be equal to $5,000:
0.04x + 0.09(100,000 - x) = 5,000
Simplifying the equation, we get:
0.04x + 9,000 - 0.09x = 5,000
Combining like terms:
-0.05x = -4,000
Dividing both sides by -0.05:
x = 80,000
Therefore, the eldest son invested $80,000 in bonds.