8th Grade > Mathematics
DIRECT AND INVERSE PROPORTIONS MCQs
:
B
Condition for direct proportionality is xy= constant and condition for inverse proportionality is xy= constant
So, the given equation y = x + 3; y is neither directly nor inversely proportional to x.
:
A
Let n be the number of boxes.
As there are 12 crayons in each box, 2400 crayons fits into
240012=200 boxes
Now the number of boxes produced will be directly proportional to time taken.
AB= Constant
A1B1 = A2B2
No. of crayons boxestime=2004=n15
So, n = 750
:
B
Let the required number of toys produced by 7 machines in 5 minutes be n.
As the time increases, the number of toys increases. Hence they are in direct proportion.
n = 490 x 5= 2450
So, 7 machines can make 2,450 toys in 5 minutes.
As the number of machines increases, number of toys increases. They are in direct proportion.
Let k is the number of toys produced by 10 machines in 5 minutes.
Then, k = 2450×107
⟹ k = 3500
So, the number of toys produced = 3,500
:
B
Expanding the given equation, we get
xy+4x=1
Here, xy=1−4x,which is not a constant. Similarly,
xy=(14y−x4),which is not a constant.
So, y is not proportional to x.
:
A
Given, two quantities x and y are said to vary in inverse proportion.
Then, x∝1y or y∝1x.
In any case, we get xy=constant
Hence the given statemnet is true.
:
A
The ratio of the length of the pole to the length of the shadow remains constant.
The length of pole and the length of the shadow are directly proportional
AB= Constant
A1B1 = A2B2
Length of polelength of shadow=560320=n500 (where n is length the second pole)
n = 875 cm
∴ the height of the pole = 875 cm
Cost of painting the pole = 875 x 5 = ₹ 4375