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Use the three given logarithms to find each value without a calculator. For numeric questions, combine the supplied rounded values; for letter questions, give an exact expression.
Download the practice pages alone, or include a separate answer key or teacher model. Longer activities may use more than one page.
Each question supplies three logarithms. Factor the target argument and use product, quotient and power laws to combine the known values. Some forms also use the fact that log base b of b equals one.
Choose any of nine forms and numeric, letter or mixed practice. Every sheet has 24 questions; mixed practice gives twelve numeric estimates followed by twelve exact letter expressions. Numeric answers use the provided rounded values, so a fresh calculator evaluation may differ.
The preview and downloaded PDF use the same resolved questions. Answers follow on separate pages; choose the student-only edition when handing out the exercise.
Learning objective
What this activity builds
Recognize products, quotients and powers in a logarithm argument, then express its value using the supplied logarithms.
Worked example
Given log base 10 of 5 is approximately 0.7 and log base 10 of 7 is approximately 0.8, estimate log base 10 of 7/125.
0.8 - 3(0.7) = -1.3, so the requested logarithm is approximately -1.3.
Recognize 125 as 5 cubed. The quotient rule gives log(7) - log(125), then the power rule gives log(7) - 3 log(5). Use the supplied rounded values.
Teaching notes
Make the practice count
Factor the target argument before using a logarithm law.
All given logarithms in a question share the same base.
Remember that the logarithm of its own base is one.
Numeric answers are estimates from the provided values, which can differ from a fresh calculator result.
Make it yours
Customize the practice
Choose your options, update the preview, then download the exact same pages.
Choose forms and numeric or letter givens. Use the supplied values without a calculator; mixed practice has twelve of each.
Expand and condense logarithms with 16 selectable product, quotient and power forms. Practice natural logs, base-ten logs and fractional powers with exact symbolic answers.
Rewrite exponential and logarithmic equations and evaluate exact logarithms. Choose numeric or symbolic forms, fractional exponents and reciprocal arguments, with separate answers.