Question

10
Example If 10 pens cost 60 rupees, what is the cost of 13 such pens?
Solution : Let us suppose the cost of 13 pens is x rupees.
The number of pens and their cost vary
13
in direct proportion. Let us express the
60
ratios and obtain an equation.
10.x = 780 (multiplying both sides by
600)
x = 78
Cost of 13 pens is 78.
Practice Set 37
1. If 7 kg onions cost 140 rupees, how much must we pay for 12 kg onions?
2. If 600 rupees buy 15 bunches of feed, how many will 1280 rupees buy?
3. For 9 cows, 13 kg 500 g of food supplement are required every day. In the same
proportion, how much will be needed for 12 cows?
4. The cost of 12 quintals of soyabean is 36,000 rupees. How much will 8 quintals cost?
3. Two mobiles cost 16,000 rupees. How much money will be required to buy 13 such
mobiles ?
Let's learn.
Inverse Proportion
Some volunteers have gathered to dig 90 pits fo
a tree plantation programme. One volunteer digs or
pit in one day. If there are 15 volunteers, they w​

Answer 1

Answer:

78 Rs

Step-by-step explanation:

Cost of 10 pens isRs 60

Cost of 1 pen 60/10

Cost of 13 pens is 60/10×13=78 Rs

Answer 2

1. Price of 12 kg onions is 240 rupees.

2. Bunches of feed in 1280 rupees is 32 bunches.

3.Food supplement required for 12 cows is 18kg.

4.Price for 8 quintals onions is 24000 rupees.

5. Price for 13 mobiles is 104000 rupees.

Step 1: Solve 1st question.

Given, price of 7kg onions= 140 rupees

Then, price of 1kg onion = $\frac{140}{7}$

                                         = $20$ rupees

Price for 12 kg onions = $20$×$12$

                                    = $240$ rupees

Step 2: Solve 2nd question.

Given, Bunches of feed in 600 rupees = 15

Then, bunches of feed in 1 rupees = $\frac{15}{600}$

                                         = $0.025$ bunches

Bunches of feed in 1280 rupees = $0.025$×$1280$

                                                      = $32$ bunches

Step 3: Solve 3rd question.

Given, food supplement required for 9 cows= 13kg 500g

                                                                      = 13500g

Then, food supplement required for 1 cows= $\frac{13500}{9}$

                                                                       = $1500$g

Food supplement required for 12 cows = $1500$×$12$

                                                                 = $18000$ g

                                                                 = $18$kg

Step 4: Solve 4th question.

Given, price of 12quintals soyabean= 36000 rupees

Then, price of 1 quintal soyabean = $\frac{36000}{12}$

                                         = $3000$ rupees

Price for 8 quintals onions = $3000$×$8$

                                    = $24000$ rupees

Step 5: Solve 5th question.

Given, price of 2 mobiles = 16000 rupees

Then, price of 1 mobile = $\frac{16000}{2}$

                                         = $8000$ rupees

Price for 13 mobiles = $8000$×$13$

                                    = $104000$ rupees