At what rate of interest must I invest a sum of money if I want to double my investment in 14 years time and if the interest is compounded annually?

Explanation: Using Texas Instruments BA II Plus:
1 ± PV: PV = -1.00
2 FV: FV = 2.00
14 N: N = 14.00
CPT I/Y: I/Y = 5.08

Using Hewlett Packard hp 12 C:
f CLEAR FIN: 0.000000000
f CLEAR REG: 0.000000000
14 n: 14.00000000
5 CHS PV: -5.00000000
15 FV: 10.00000000
i: 5.07566387

Note: You can put in any value for PV as long as you put in twice this value for FV.