Hi

oasis90,

at a rate of (exact rate) => at a rate of 5%, at a rate of 10 cents per mile, at a rate of 40 km/h, at a rate of a foot per year

at a rate (comparison: x times/double/triple) => cats age at a rate three times that of dogs, paintings appreciate at a rate 10 times that of sculptures

So, in your example, "at a rate of five times that ..." is wrong because this is a comparison, not an exact rate.

Best, Jennifer

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