Although you said the variance is 120, I suspect you meant to say standard deviation. If that's the case, then
P(970 < x < 1320)
= P((970 - 1250)/120 < (x - 1250)/120 < (1320 - 1250)/120)
≈ P(-2.3333 < z < 0.5833)
= P(z < 0.5833) - P(z < -2.3333)
≈ 0.72012 - 0.009815
≈ 0.7104
If you really did mean variance, then
P(970 < x < 1320)
= P((970 - 1250)/√120 < (x - 1250)/√120 < (1320 - 1250)/√120)
≈ P(-25.5604 < z < 6.3901)
= P(z < 6.3901) - P(z < -25.5604)
≈ 1 - 0
≈ 1
