Hi
Normal Distribution: µ = 490 and σ = 100
Using TI or similarly an inexpensive calculator like a Casio fx-115 ES plus
Continuous curve
P(390 > x > 590)= normalcdf(390, 590, 490, 100) = .6827 0r 68% (2 decimal places)
Keisan Online Calculator
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P(-1.3 > z > 8.99)= normalcdf(-1.3, 8.99, 0, 1) = .90 (2 decimal places)
Important You feel comfortable using Your calculator.
Wish You the Best in your Studies.
standard Normal Curve: µ = 0 and σ = 1
various z-values given