A school has 9 periods a day each of 40 minutes duration. How long would each period be, if the school has 8 periods a day, assuming the number of school-hours to be the same?

In a direct proportion, two quantities x and y vary with each other such that:

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• 

• xy remains constant

In a direct proportion, two quantities x and y vary with each other such that:

• 
• 

• xy remains constant

Let there be two values of x be x₁ and x₂ such that two values of y as y₁ and y₂ respectively equal to x₁ and x₂, then x and y are said to vary in inverse proportion, if:

If the following quantities vary directly, then what is the value of x?

• x = 4

•  x = 7

• x = 28

If the following quantities vary directly, then what is the value of y?

• y = 20

• y = 2

• y = 4

If x and y vary in direct variation, then what is the value of x corresponding to the value of y as 16?

• x = 1

• x = 4

• x = 6

If x and y very indirectly, then what is the value of x when y = 10?

• x = 10

• x = 20

• x = 15

For inverse variation what is the value of x when y = 20?

• x = 4

• x = 5

• x = 3