When two lights blink in alternation close together, we perceive one light moving back and forth if the time between blinks is short. We want to know the longest interval of time between blinks that preserves this illusion of motion? We ask subjects to turn a knob that slows the blinking until they "see" two lights rather than one light moving. A report gives the results in the form "mean plus or minus the standard error of the mean." Data for 20 subjects are summarized as 259±45 (in milliseconds). What are x¯¯¯ and s for these subjects? (This exercise is also a warning to read carefully: that 259±45 is not a confidence interval, yet summaries in this form are common in scientific reports.)

mujhko hui na

answer: c

step-by-step explanation

the cross section of an object is the shape you get when you cut straight through an object.

thus the cross section of the human hair is a circle. hence the cross sectional area is the area of a circle and area of circle is :

a = 3.14 × r²

we are given that the average width of human hair is = 4 × (1 / 10³) cm.

so the diameter of the circle is = 4 × (1 / 10³) cm.

∴ radius r = (diameter/2) = 2 × (1/10³) cm

now area a = 3.14 × (2 × (1/10³))² cm²

scientific notation is a standard way of writing very large and very small numbers so that they’re easier to both compare and use in computations. to write in scientific notation, follow the form

n × 10 ᵃ

where n is a number between 1 and 10, but not 10 itself, and a is an integer (positive or negative number).

so area can be rewritten in scientific notation as :

⇒ 3.14 × 4 × (1/10⁶)

⇒ 12.56 × 10 ⁻⁶ cm²

⇒1.256 × 10⁻⁷ cm²