Investment End of Chapter Problem a. How does the opportunity cost principle explain the relationship between the real interest rate and inves As the interest rate rises, Othe more spending businesses want to do. the more attractive it is to leave money in the bank instead of spending on investments. it has no effect on investment spending. If firms need to expand, they will invest regardless of the in the less attractive it is to leave money in the bank instead of spending on investments. b. The investment line is because of the relationship between real interest rates and investment s