LogarithmsFinding the number
Name: Date:
Find the missing number in each logarithm.
1log₂ = 7
2log₂ = 3
3log₃ = 4
4log₇ = 3
5log₃ = 3
6log₃ = 6
7log₄ = 2
8log₂ = 9
9log₅ = 3
10log₃ = 5
Find the number in a logarithm worksheets
If log₂ of some number is 7, what is the number? These free printable worksheets ask that question ten times a page, and the way to answer it is the most useful fact about logarithms: a logarithm and a power say the same thing.
If they get stuck
Find the number in a logarithm
The answer key prints on a separate page.
What's on this sheet
log₂ __ = 7 is the sentence 2⁷ = __ written another way. Once a student can move between the two forms, the question is just a power to work out, and 2⁷ is 128. Everything else about logarithms depends on this one move, and this page gives it a good amount of practice on its own.
Why this sheet works
The usual mistake is to multiply the two numbers. log₂ __ = 7 turns into 14, and log₃ __ = 4 into 12. Both of those answers can be checked and thrown out straight away: 2 to what power gives 14? No whole number does. A student who checks a few of these by going back to the power soon stops making the mistake.
How this one works
log₂ 128
2⁷ = 128
- A logarithm names a power. log₂ of a number is 7 when that number IS the 7th power of 2.