CAT Question – Logarithms

This is a reasonably tough question. But since the messrs conducting CAT seem to have upped the ante on Logarithm, this is probably par for the course


log5x = a (This should be read as log X to the base 5 equals a)log20x = b
What is
logx10 ?
Correct Answer: (a + b)/2abExplanation

log5x = a
log20x = b
logx5 = 1/a

logx20 = 1/b
logx100/5 = 1/b
logx100 – logn5 = 1/b
2logx10 – 1/a = 1/b
logx10 = ½(1/a + 1/b)
logx10 = (a + b)/2ab

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