2.- 14 solution: x accounts for two tenths, y accounts for three tenths and z accounts for five tenths. It is obtained by 3x-3y+z=4, and the total number is 20, so that X, Y, Z, Y, Z can be obtained and substituted.

3.5 Solution: The first power of 7 is 7, the second power is 9, the third power is 3, the fourth power is 1, and the fifth power is 7. Find the period. 2004 can be divisible by 4, so it is exactly a whole period, that is, the last power of 2004 7 is 1, plus 2004, it is 5.

4. Solution: Write the 55th power of 3 as: 1 1 power (the 5th power of 3), which is similar to one time. Write the 44th power of 4 and the 33rd power of 5 in this form, and directly compare the 5th power of 3, the 4th power of 4 and the 3rd power of 5.