probability (area under the curve)

0.6827

That is 68.27% of the distribution.

Steps

  1. 1.standardize: z = (x - 100) / 15
  2. 2.z for 85: -1; z for 115: 1
  3. 3.area between: 0.8413 - 0.1587 = 0.6827

Normal distribution calculator (area under curve) · free from StatsLearn