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Math Help - Could someone check my answers pls.

  1. #1
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    Could someone check my answers pls.

    The rails on a railroad are built from thirty- foot sections. When a train wheel passes over the junction between two sections, there is an audible click. Inside a train that is traveling at 70mph, how many clicks will a passenger hear each twenty seconds?

    30 clicks

    In attempting to calculate the carrying capacity of a cylindrical pipe, Avery measured the outer diameter to be 2 inches, neglecting to notice that the pipe was one eighth of an inch thick. By what percent did Avery overestimate the carrying capacity of the pipe?

    24%

    Thanks.

    Vicky.
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  2. #2
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    Hello Vicky
    Quote Originally Posted by Vicky1997 View Post
    The rails on a railroad are built from thirty- foot sections. When a train wheel passes over the junction between two sections, there is an audible click. Inside a train that is traveling at 70mph, how many clicks will a passenger hear each twenty seconds?

    30 clicks
    I make the answer about 68.

    70 mph = \frac{70 \times 5280}{3600} feet per sec

    So in 20 sec the train passes over \frac{70 \times 5280\times 20}{3600\times 30} thirty-foot sections, which is a bit more than 68.


    In attempting to calculate the carrying capacity of a cylindrical pipe, Avery measured the outer diameter to be 2 inches, neglecting to notice that the pipe was one eighth of an inch thick. By what percent did Avery overestimate the carrying capacity of the pipe?

    24%

    Thanks.

    Vicky.
    I make it just over 30%.

    The inner diameter is 1\tfrac34 = 1.75 inches. The carrying capacity is proportional to the area of the cross-section, which in turn is proportional to the square of the diameter. So by using 2 in instead of 1.75 in, the area is overestimated in the ratio 2^2:1.75^2, or by a factor of \frac{2^2}{1.75^2}= 1.306 = 1 + 0.306 (3 d.p.)

    So Avery has overestimated by about 30.6%

    Grandad
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  3. #3
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    Thank you!!!

    Vicky.
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