According to the rule of 72, mc007-1.jpg which statement is true? 1. an investment of $3,100 will double in 12 years at a compound interest rate of 5%. 2.an investment of $9,000 will double in 10 years at a compound interest rate of 7%. 3. an investment of $4,500 will double in 8 years at a compound interest rate of 9%. 4. an investment of $3,000 will double in 4 years at a compound interest rate of 12%.