Any investments under the provisions of §§ 4-5-12 to 4-5-39, inclusive, shall be made with the exercise of that degree of judgment and care, under circumstances then prevailing, which persons of prudence, discretion, and intelligence exercise in the management of their own affairs, not for speculation but for investment, considering the probable safety of their capital as well as the probable income to be derived.
SDCL 4-5-27