Use the Pythagoras Theorem in the corresponding right angled triangles.
Answer:
sine 23 = x/21
Multiply both sides by 21
21 x sine 23 = x
Now, use a calculator and find the answer of the 21 times the sine of 23:
x = -17.7706284876
Answer:
12 students
Step-by-step explanation:
Given

Required
Determine the number of students that eat lunch once a week
In Sets;
If out of 9, at least 7 eats one a week then
9 - 7 eats lunch once a week

<em>In other words;</em>
2 out of 9 students eat lunch once a week
Number of students in this category is then calculated as thus;



