70 mph = feet per sec
So in 20 sec the train passes over thirty-foot sections, which is a bit more than 68.
I make it just over 30%.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?
The inner diameter is 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 , or by a factor of (3 d.p.)
So Avery has overestimated by about 30.6%