Find the probability that more than 70% of the sampled teenagers own a smartphone?

Question

Smartphones: A Pew Research report indicated that 73% of teenagers aged 13–17 own smartphones. A random sample of 150 teenagers is drawn.

Find the probability that more than 70% of the sampled teenagers own a smartphone

Answer 1

use formula z = (phat - p)/sqrt(p * (1-p)/n) were phat = 0.70, p = 0.73 and n = 150

z = (0.70 - 0.73)/sqrt(0.73 * 0.27/150) = -0.83

P(phat > 0.70) = P(z > -0.83) = P(z < 0.83) = 0.7967