book Maths Puzzle Numerical Ability

The decibel level of sound is given by D=10log(I/10^-12)where I is the
sound intensity measured in watts per square meter. Find the
decibel level of a whisper at an intensity of

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book Other Question

I am truly stumped with this one.

An alloy weighing 20 kg is 30% copper. How many kg of another alloy, which is 80% copper, must be added in order to produce an alloy which is to be 50% copper?
Given: In triangle ABC, angle B=120 degrees
Prove: angle A is not equal to 60 degrees
Plan: use and indirect proof. use the paragraph method to write it.