 In this video we provide the solution to question number 8 for practice exam 4 for math 1050, in which case we have to compute log base 2 of 125 times log base 5 of 2. And so this is actually a situation where the change of base form can be very useful. So if I turn both of these into the natural log, log base 2 of 125 becomes the natural log of 125 over the natural log of 2. And then log base 5 of 2, that becomes the natural log of 2 over the natural log of 5, like so. So I'm going to swap the denominators because it's just multiplication and commutes. So we get the natural log of 125 over the natural log of 5, and that's then multiplied by the natural log of 2 over the natural log of 2. Notice that those actually just cancel out entirely. And what we're left with the natural log of 125 over the natural log of 5, I can rewrite that as the log base 5 of 125, like so. And so I'm looking for what power of 5 gives you 125. Well 125 is 5 cubed, so this is going to give us 3. And so therefore the correct answer I wrote over it would then be choice D right there.