中2數學 3條炸,幫幫忙丫

1)May is 5 feet 2 inches tall.t is known that 1 feet=12inches,1 inches=2.54cm,calcul ate his height in cm.(Correct the answer to 3 sig.fig)
5 feet 2 inches
=[5(12)+2]inches
=62inches
=62(2.54)cm
=157.48
=157cm(Correct the answer to 3 sig.fig)
2)A train takes 5 hours to travel from City A to Cty B at a speed of 60km/h.If the speed increases to 90km/h,how long does it take?(Correct the answer to 2 sig.fig.)
the distance between City A and City B = 5(60)=300km
the time taken
=300/90
=3.33333
=3.3 hours (Correct the answer to 2 sig.fig.)
3)In an experment,the thickness of a piece of paper is measured to be 0.017 mm with a relative error of 1/34.Find the range of its true thickness.
the percentage error =1/34 * 100%~2.94%
the absolute error = 0.017 * 2.94%~0.0005mm
the maximum thinkness=0.017+0.0005=0.0175mm
the minimum thinkness=0.017-0.0005=0.0165mm
Therefore , the range of its true thickness lies between 0.0165mm and 0.0175mm

1) May's height is:
(5x12+2)inch
=(62x2.54)cm
=157.48cm
=157cm(corr to 3 sig fig)

2) The time taken is:
(5x60)/90
=3.3hour(corr to 2 sig fig)

3) 0.017/34
=0.0005mm
∵the maximum error is 0.0005mm
∴the range is 0.0175-0.0165mm

p.s. "/" means divided by

2007-11-25 13:50:26 補充：
maximum thinkness=0.017+0.0005=0.0175mmminimum thinkness=0.017-0.0005=0.0165mm∴the range is 0.0175-0.0165mm

1. May's height = (5 x 12 + 2) x 2.54
= 62 x 2.54
= 157(3 sig. fig.)

2. let y hours be the time that the train takes
5 x 60 = y x 90
300 = 90y
y = 3.3
∴ the train takes 3.3 hours

3. let the absolute error be y mm
y/0.017 = 0.34
y = 0.00578
∴the range of the true thickness is 0.02278, 0.01122