SPOILER KAPLAN FULL LENGTH 5

[darrarch]

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Okay I am terrible at math. Can someone please break down this math better than the explanation? How they solved this without calculator. Possibly anyway you thought of this problem. In the passage the equation I/I0=e^-uk and it was stated that anything less than 1%of incidence radiation transmission was considered safe.

 

[Philly145]

Value of e is about 2.7, they are rounding this to 3.

From the table, the value of u at 50keV for lead is 9.11.

The formula is [% transferred]=3^(-9.11*x)

x is the distance listed in each of the answers.

For (A): 3^(-9.11*.1) ----> round -9.11 to -10 and you get 3^(-10*.1) ----> 3^(-1) = 1/3 = 33% of the xrays are going through the lead. This is more than the 1% safe limit from the passage.

(B): 3^(-9.11*3) -----> 3^(-27)% of the xrays are going through the substance. This is much less than 1%. This is the answer because it's the minimum distance below the 1% threshold.

Don't be afraid to round every number you see in a question to the nearest whole number.