Which statement about simple interest and compound interest is correct?

Group of answer choices:

1. Simple interest and compound interest are both the interest per period is charged on the principal plus any accumulated interest. They just use different interest calculation formulas.

2. Compound Interest is the interest per period is always charged only on the principal. Simple interest is the interest per period is charged on the principal plus any accumulated interest.

3. Simple Interest is the interest per period is always charged only on the principal. Compound interest is the interest per period is charged on the principal plus any accumulated interest.