S.chand Class 8 Maths Solution Chapter 10 Variation and Direct and Inverse Proportions Exercise 10 A

 Exercise 10 A

In which of the following, x and y vary directly with each other. For each direct variation, state the constant of variation.

Question 1

1. $y=-8 x$

2. $y=\frac{3}{4} x$

3. $x y=5$

4. $y=\frac{3}{x}$

5. $y+4 x=0$

6. $y-3 x=1$

7.

x	1	2	3	4
y	-5	-10	-15	-20

8.

x	2	4	6	8
y	-1	2	-3	4

9. The height to which a balloon with hydrogen gas rises in the air varies directly as time. Given below are some observations about the time and the corresponding height of the balloon (in metres). Find the missing terms in the table.

Time (in minutes)	3	4	__	25	__
Height of the balloon (in meter)	__	48	84	__	1860

10. If $d$ varies directly as $t$, and if $d=4$ when $t=9$, find $d$ when $t=21$.

11. The mass of a uniform copper bar varies directly as its length. If a bar $40 \mathrm{~cm}$ long has a mass of approximately $420 \mathrm{~g}$, find the mass of a bar $136 \mathrm{~cm}$ long.

12. A fish with a mass of $3 \mathrm{~kg}$ causes a fishing pole to bend $9 \mathrm{~cm}$. If the amount of bending varies directly as the mass, how much will the pole bend for a $2 \mathrm{~kg}$ fish ?

13. At a party, 8 bottles of soft drink are served for every batch of 5 children. How many bottles would be served if 40 children were present at the party ?

14. Harsh takes 150 steps in walking a distance of 125 metres. What distance would he cover in 360 steps ?

15. The second class railway fare for $240 \mathrm{~km}$ of journey is $₹ 15.00$. What would be the fare for a journey of $139.2 \mathrm{~km}$ ? Assume that the fare varies directly as the length of the journey.