Arrange the following intervals of standard normal variate in increasing order of probabilities.

1.0 ≤ Z ≤ +1

2.+1 ≤ Z ≤ +2

3.+2 ≤ Z ≤ +3

4.+3 ≤ Z < +∞

A4, 3, 2, 1 ✓ Correct

B3, 2, 1, 4

C2, 1, 3, 4

D1, 2, 3, 4

Correct answer: (A) 4, 3, 2, 1

Explanation

The intervals hold shrinking probabilities of about 0.34, 0.14, 0.02 and 0.001 as one moves outward from the mean.

The band beyond +3 has the smallest probability near 0.001, so interval four comes first.

The band +2 to +3 holds about 0.02, placing interval three next.

The band +1 to +2 holds about 0.14, and the band 0 to +1 holds about 0.34, the largest.

In increasing order of probability the sequence is four, three, two, one.

The bulk of a normal curve's area clusters near the mean and thins in the tails.

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