Solution: Let the original length of the spring be xcm and the forward coefficient be KN/m. According to the meaning of the question, we can get:

k( 16.4-x)=2 ①

k( 17.9-x)=5 ②

According to formula ①, k=2/( 16.4-x) ③.

Substitute ③ into ② to get:

3x=46.2

Then x= 15.4.

Answer: The spring should be15.4cm..

10. solution: let x, y and z be 1 angle, and the sum of 5 angles 1 yuan.

Judging from the meaning of the question:

X+5Y+ 10Z=70 ①

X+Y+Z= 15 ②

If x is removed, 4y+9z=55.

z=(55-4y)/9=6+( 1-4y)/9

y=7。

Or x=(55-9z)/4= 13+(3-9z)/4.

z=3。

∴x=5,y=7,z=3.

Answer: Take 5 yuan 1 corner, 5 cents and 1 yuan, which are 7 yuan and 3 yuan respectively.

1 1.

Solution: Let the uphill journey be xkm and the downhill journey be ykm, then the flat road has (3.3-x-y)km, and the equation can be obtained.

x/3+y/5+(3.3-x-y)/4 = 5 1/60

x/5+y/3+(3.3-x-y)/4=53.4/60

X= 1.2 y= 1.5。

∴ The flat slope distance is 3.3- 1.2- 1.5=0.6 (km).

A: The distances from A to B are 1.2km, 0.6km and 1.5km respectively.