Review question

# Can we evaluate these log expressions without using a calculator? Add to your resource collection Remove from your resource collection Add notes to this resource View your notes for this resource

Ref: R9976

## Suggestion

1. Without using tables [or calculators], find the value of \begin{align*} 2 \lg 5 - \frac{1}{2} &\lg 9 + \lg 0.12.\\ [\lg x &= \log_{10} x] \end{align*}

If we can’t use calculators, we have to simplify this expression. So what rules and identities do we know for logarithms?

1. If $\lg 2 = 0.30103$ and $\lg 3 = 0.47712$, find, without using tables [or calculators], the values of $\lg 6$ and $\lg 15$.

How could we rewrite the required logarithms in terms of the logarithms we are given? Remember that all logarithms are to base 10!