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Online Quiz (Worksheet A B C D)

Questions Per Quiz = 2 4 6 8 10

Grade 8 - Mathematics
2.10 Inverse Proportion - I

  • If two variables x and y vary such that xy = constant(k). Then x and y are said to vary inversely or are in inverse variation.
  • If y varies inversely x, then directly as 1/x.
  • And x varies directly as 1/y.
  • Or, if x and y vary inversely, then x 1/y or y 1/x.
Example:
x is varies inversely y and constant of variation is 1/2, find x when y = 5, find y when x = 1/4.
Solution:
Since x is varies inversely y
We have x.y = k, given that k = 1/2.
\ xy = 1/2
If y = 5 x.5 = 1/2 x = 1/10.
If x = 1/4 1/4 . y = 1/2 y 1/2 * 4 = 2

Example:
If 3 men can paint a house in 2 days, how long will it take 2 men to do the same job?.
Solution:
This is an inverse relationship. The fewer men, the more days it will take to paint the house.
3:2 :: 2:x
or
3/2 = 2/x
Cross multiplying
3x = 4
x = 4/3 = 1 1/3
Answer: 1 1/3 days


Directions: Solve the following problems. Also write at least 10 examples of your own.
Q 1: You have enough milk to feed 90 children for 4 days. If 10 of the children do not drink milk, how many days will the supply last?
3 1/8
4 1/2
2 3/4
6

Q 2: A gear with 20 teeth revolving at 200 revolutions per minute is meshed with a second gear turning at 250 revolutions per minute. How many teeth does this gear have?
18
16
12
25

Q 3: x is varies inversely y and constant of variation is 7, find y when x = 9.
7
7/9
9
9/7

Q 4: A field can be plowed by 8 machines in 6 hours. If 5 machines are broken and cannot be used, how many hours will it take to plow the field?
7 2/3
10 1/2
8
9 3/5

Q 5: x is varies inversely y and constant of variation is 21/4, find y when x = 7.
4/3
3
4
3/4

Q 6: Two boys weighing 60 pounds and 80 pounds balance a seesaw. How many feet from the fulcrum must the heavier boy sit if the lighter boy is 8 feet from the fulcrum? (Hint: Weight times distance from fulcrum remains constant.)
12
5
6
8

Q 7: x is varies inversely y and constant of variation is 2/3, find x when y = 7.
21
21/2
2/21
2

Q 8: x is varies inversely y and constant of variation is 7/5, find x when y = 7.
5
1/5
None of these
1

Question 9: This question is available to subscribers only!

Question 10: This question is available to subscribers only!


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