In October 1991, the Sacramento City Council adopted a law to reduce the allowed

Question

In October 1991, the Sacramento City Council adopted a law to reduce the allowed sound intensity level of the much despised leaf blowers from their current level of about 95 dB to 70 dB by May 1992.
With the new law, what is the ratio of the new allowed intensity to the previously allowed intensity?

Here's what i tried:
starting with the following equation- = 10 log I/I0

i plugged in the numbers- 95-70 = 10 log I/I0 --->    2.5 = log I/I0 ----> I/I0 = 10^2.5 = 316.23

thus the new ratio should be 316.23  

This answer is incorrect, however. What am i doing wrong?   

Explanation / Answer

Prevous allowed intensity level L = 95 dB      L = 10 log ( I / Io)     95 = 10 log ( I / Io)    9.5 = log( I / Io) I /Io = 10^9.5 I = Io * 10^9.5    = 10^-12 * 10^9.5    = 10^-2.5   W / m^ 2 New allowed intensity level L ' = 70 dB      L ' = 10 log ( I '/ Io)     70 = 10 log ( I ' / Io)    7 = log( I ' / Io) I ' /Io = 10^7 I ' = Io * 10^7    = 10^-12 * 10^7    = 10^-5   W / m^ 2 the ratio of the new allowed intensity to the previously allowed intensity = I ' / I                            = 10^-5 / 10^-2.5                            = 10^-2.5                            = 3.162*10^-3    New allowed intensity level L ' = 70 dB      L ' = 10 log ( I '/ Io)     70 = 10 log ( I ' / Io)    7 = log( I ' / Io) I ' /Io = 10^7 I ' = Io * 10^7    = 10^-12 * 10^7    = 10^-5   W / m^ 2 the ratio of the new allowed intensity to the previously allowed intensity = I ' / I                            = 10^-5 / 10^-2.5                            = 10^-2.5                            = 3.162*10^-3      

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