A student has an average of 65 on three tests. What does that student need to make on the fourth test to bring the average to 70? Well, when you look at that, does that mean that the student made a 65 on each of the three tests? It just means that at that point, they averaged 65. So, for our math's sake, It could mean that we just say we can put a 65 in there, and it'll all average out to be the same grade. So you've got a 65 on the first test.
You have a 65 on the second test and a 65 on the third test. Again, they just averaged that. This one could be a little higher, could be a little lower, but when you add them up and divide by three, it still comes out to be 65. Now the question is... What do you have to make on that fourth test?
So that's the unknown. So that when I add those up and now divide by 4, I have an average of 70. So the way you want to work this problem, just like we did all of the exercises in the previous section, you notice I've got multiple. terms up here.
So what I would recommend is put all this in parentheses, put this over 1, and answer, what's my common denominator? You say 4. So you put a 4 here, and a 4 here. You build up this fraction. Once you've got the denominators the same, it's the numerators that should be equal.
So we've got 65, 65, 65 and x is equal to 280. So 65 three times, let's see, what is that? That would be, add those up, 5, 10, 15, carry the 1. That's 195. So subtract that 195. And it looks like that fourth test, your unknown here, is going to be, let's see, that'd be 10 minus 5, 27, 85. You need to make an 85 on that fourth test so that when you add those up, divide by 4, you have a 70.