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A scientist is weighing each of 30 fishes. Their mean weight worked out is 30 gm and a standard deviation of 2 gm. Later, it was found that the measuring scale was misaligned and always under reported every fish weight by 2 gm. The correct mean and standard deviation (in gm) of fishes are respectively:

1. 32,2
2. 32,4
3. 28,2
4. 28,4

Correct answer: 32,2

Solution

Each reading is 2 g too low, so the true weight is reading + 2. Adding a constant shifts the mean to 30 + 2 = 32 g while leaving the standard deviation unchanged at 2 g.

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