WEBVTT
1
00:00:00.000 --> 00:00:03.600
Hey, this is Mr. Preze again.
2
00:00:03.600 --> 00:00:07.040
Okay, Charlie, let's get to work right there.
3
00:00:07.040 --> 00:00:09.760
A math professor, servitor class,
4
00:00:09.760 --> 00:00:13.000
and found that the ratio of students
5
00:00:13.000 --> 00:00:15.280
who use the school's tutoring service
6
00:00:15.280 --> 00:00:18.800
to those who do not is three to eight.
7
00:00:18.800 --> 00:00:22.720
The number of students who did not use the tutoring lab
8
00:00:22.720 --> 00:00:26.360
was 15 more than the numbers who did.
9
00:00:27.840 --> 00:00:29.760
How many students use the service
10
00:00:29.760 --> 00:00:31.520
and how many do not?
11
00:00:32.800 --> 00:00:34.360
Okay, just relax.
12
00:00:36.720 --> 00:00:39.520
Let's begin by letting X represent
13
00:00:39.520 --> 00:00:43.640
the number of students who use the tutoring service.
14
00:00:43.640 --> 00:00:46.760
Since we were told that there are 15 more
15
00:00:46.760 --> 00:00:48.640
who do not use the service,
16
00:00:48.640 --> 00:00:53.160
we can say X plus 15 is equal to the number of students
17
00:00:53.160 --> 00:00:55.760
who do not use the tutoring service.
18
00:00:55.760 --> 00:00:59.880
Now, from the information up there,
19
00:00:59.880 --> 00:01:03.240
we were given that the ratio of those who do
20
00:01:03.240 --> 00:01:06.000
to those who do not is three to eight.
21
00:01:06.000 --> 00:01:11.400
And that must equal the ratio of X to X plus 15.
22
00:01:11.400 --> 00:01:13.440
This gives us our proportion.
23
00:01:15.280 --> 00:01:17.520
Okay, let's move our work over here.
24
00:01:17.520 --> 00:01:19.400
Remember, X represents the number of students
25
00:01:19.400 --> 00:01:23.160
who use the service, X plus 15 represents
26
00:01:23.160 --> 00:01:26.160
the number of students who do not use the service.
27
00:01:26.160 --> 00:01:27.880
There's our proportion problem.
28
00:01:27.880 --> 00:01:31.480
Now, we can use a technique called cross multiplication
29
00:01:31.480 --> 00:01:33.080
to solve our proportion.
30
00:01:33.080 --> 00:01:34.320
So here we go, Charlie.
31
00:01:34.320 --> 00:01:37.280
Let's cross multiply this way and what'd you get?
32
00:01:37.280 --> 00:01:38.640
Three times let's put the team.
33
00:01:38.640 --> 00:01:39.960
Very nice there, Charlie.
34
00:01:39.960 --> 00:01:42.440
Now, let's go the other way and what'd you get?
35
00:01:42.440 --> 00:01:43.840
AX.
36
00:01:43.840 --> 00:01:45.320
Very nice there, Charlie.
37
00:01:45.320 --> 00:01:49.520
Now, on the left hand side, let's distribute the three through
38
00:01:49.520 --> 00:01:54.000
so we get three X plus 45 equals eight X.
39
00:01:54.960 --> 00:01:57.000
Let's put our work up there.
40
00:01:57.000 --> 00:02:00.960
Now, to solve for X, we'll subtract three X from both sides,
41
00:02:02.040 --> 00:02:06.640
giving us 45 equals five X.
42
00:02:06.640 --> 00:02:09.640
Now, to solve for X, we'll divide both sides by five
43
00:02:10.640 --> 00:02:14.760
and that gives us nine is equal to X.
44
00:02:16.040 --> 00:02:18.200
Now, if X equals nine,
45
00:02:18.200 --> 00:02:21.520
that represents the number of students who use the service
46
00:02:21.520 --> 00:02:25.360
and remember there was 15 more who do not,
47
00:02:25.360 --> 00:02:28.440
therefore we get X plus 15 equals 24,
48
00:02:28.440 --> 00:02:29.880
which represents the number of students
49
00:02:29.880 --> 00:02:32.640
who do not use the tutoring service.
50
00:02:32.640 --> 00:02:34.760
So let's go ahead and summarize our answer.
51
00:02:34.760 --> 00:02:37.840
Remember, X was nine, therefore nine students
52
00:02:37.840 --> 00:02:39.640
use this tutoring service.
53
00:02:41.040 --> 00:02:44.880
And if X is nine, nine plus 15 is 24
54
00:02:44.880 --> 00:02:47.720
and therefore 24 do not.
55
00:02:47.720 --> 00:02:49.920
Don't forget to circle or box your answer.
56
00:02:49.920 --> 00:02:54.080
Now, I always encourage that you all use the tutoring service,
57
00:02:54.080 --> 00:02:55.560
especially him.
58
00:02:55.560 --> 00:02:56.320
What?
59
00:02:56.320 --> 00:02:57.600
Never mind, Charlie.
60
00:02:57.600 --> 00:03:26.400
We'll see you all again soon.