Answer
The researcher needs to sample another 111 teenagers.
Work Step by Step
$p=0.95=95$%
We must have:
$np(1-p)\geq10$
$n0.95(1-0.05)\geq10$
$n\geq\frac{10}{0.95\times0.05}=210.526$
$n\geq211$ (The number of teenagers must be an integer)
But, the researcher sampled 100 teenagers. So, the researcher needs to sample another: $211-100=111$ teenagers.
