Estimate Angles
In order to estimate a given angle, keep in mind a 90° angle (right angle).
A 90° angle looks like a corner of a rectangular piece of paper or a corner of a square.
Let's look at an example.
Consider the angle given below.
Let's estimate the measure of this angle.
Observe that, the size of this angle is less than 90°.
The size of this angle is
1 2
of the size of a right angle.

×  90°  =  45° 
So, the estimate for the measure of the given angle is 45°.
ds
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Help
The correct answer is
Remember :
The smallest number is the one that comes first while counting.
Solution :
To arrange the given numbers in order from smallest to greatest, find the smallest number among all the given numbers.
21,27,23
21 is the smallest number.