On a graph with a logarithmic horizontal axis, which value is closest to the one represented by the position exactly midway between the 10 and 100 tick marks?

Answer: C. About 32

On a logarithmic scale, position is proportional to the logarithm of the value. The midpoint between log₁₀10 = 1 and log₁₀100 = 2 is 1.5, so the value is 10 to the power 1.5, i.e. √1000 ≈ 31.6. Similarly, within one decade, 2 lies at about 30% and 5 at about 70% of the width. Many datasheet graphs, such as frequency responses and SOA, have logarithmic axes; the tick spacing is not uniform, so reading them with a linear intuition leads to large misreadings. 55 is the arithmetic mean of 10 and 100, the midpoint on a linear scale.