WEBVTT
00:00:00.500 --> 00:00:03.610
Estimate the following: 21 percent of 50.
00:00:04.420 --> 00:00:07.980
A good example of needing to use this in real life is going out to eat.
00:00:08.620 --> 00:00:12.980
When calculating a tip, we are supposed to take the bill amount and multiply it by a percentage.
00:00:13.670 --> 00:00:17.530
And the tip amount is up to us, usually between 15 and 20 percent.
00:00:18.180 --> 00:00:19.810
Now notice it says to estimate.
00:00:20.360 --> 00:00:27.080
So instead of using 21 percent, we can estimate using a number that’s a little easier to work with, 20 percent.
00:00:27.770 --> 00:00:30.400
Now the word “of” in mathematics means to multiply.
00:00:30.900 --> 00:00:39.890
So 20 percent times 50, 20 percent we can rewrite as 20 out of 100 and 50 we can rewrite as 50 over one.
00:00:40.750 --> 00:00:44.630
Now since we’re estimating, maybe we didn’t have a calculator.
00:00:44.990 --> 00:00:52.990
So instead of multiplying straight across and have a very large numbers, we can simplify here, actually two different options of simplifying.
00:00:53.830 --> 00:00:56.190
We can simplify the 20 into the 100.
00:00:56.310 --> 00:01:04.590
Or we can simplify the 50 into the 100 because we can take a number on the top and simplify it with a number on the bottom.
00:01:05.760 --> 00:01:06.890
Let’s say we did 20.
00:01:07.200 --> 00:01:11.030
20 goes into itself once and goes into 100 five times.
00:01:12.890 --> 00:01:15.410
50 times one on the numerators is 50.
00:01:15.500 --> 00:01:17.870
And five times one on the denominators is five.
00:01:17.940 --> 00:01:20.200
And 50 divided by five is 10.
00:01:20.790 --> 00:01:24.780
Now let’s say we simplify the 50 in the 100 instead.
00:01:25.490 --> 00:01:28.410
50 goes into itself once and 100 twice.
00:01:28.810 --> 00:01:31.680
So on the numerators, 20 times one is 20.
00:01:32.070 --> 00:01:34.180
And on the denominators, two times one is two.
00:01:34.390 --> 00:01:36.770
And 20 divided by two is again 10.
00:01:37.460 --> 00:01:39.230
Therefore, our estimate is 10.