Weigh it, Pour it — NCERT Solutions

Answer (sample):

1. A bag of rice — approximately 10 kg
2. A bucket full of water — approximately 10–15 kg
3. A suitcase full of clothes — approximately 8–10 kg

(Students should write objects that require effort to lift and estimate their weights.)

Concept: Number of 1 kg packets $= \dfrac{\text{Total weight in kg}}{1\ \text{kg}}$

(a) 10 kg:
$$\frac{10\ \text{kg}}{1\ \text{kg}} = \mathbf{10}\ \text{packets}$$

(b) 20 kg:
$$\frac{20\ \text{kg}}{1\ \text{kg}} = \mathbf{20}\ \text{packets}$$

(c) 50 kg:
$$\frac{50\ \text{kg}}{1\ \text{kg}} = \mathbf{50}\ \text{packets}$$

(d) 25 kg:
$$\frac{25\ \text{kg}}{1\ \text{kg}} = \mathbf{25}\ \text{packets}$$

Concept: We match each object with its realistic estimated weight.

Correct Matching:

Reasoning:

• A leaf is very light → 1 g to 5 g
• A pen is light → 10 g to 15 g
• A filled 1 litre bottle → about 1 kg (800 g–1000 g)
• A cat → 3 kg to 5 kg
• A wooden chair → 6 kg to 10 kg
• An empty gas cylinder → about 15 kg
• A tiger → 150 kg to 300 kg
• An elephant → more than 1000 kg

Answer (sample):

(Students should look around their home and write the names of actual containers they find.)

Given: Capacity of 1 bottle = 500 ml; Capacity of large bottle = 1 l = 1000 ml

Step 1: $500\ \text{ml} + 500\ \text{ml} = 1000\ \text{ml} = 1\ \text{l}$

Step 2: Number of 500 ml bottles $= \dfrac{1000}{500} = 2$

$$\boxed{2\ \text{bottles of 500 ml will fill a 1 l bottle.}}$$

Also: $500\ \text{ml} = \dfrac{1}{2}\ \text{l}$

Given: Capacity of 1 bottle = 250 ml; Capacity of large bottle = 1 l = 1000 ml

Step 1: $250 + 250 + 250 + 250 = 1000\ \text{ml} = 1\ \text{l}$

Step 2: Number of 250 ml bottles $= \dfrac{1000}{250} = 4$

$$\boxed{4\ \text{bottles of 250 ml will fill a 1 l bottle.}}$$

Also: $250\ \text{ml} = \dfrac{1}{4}\ \text{l}$

Given: Capacity of 1 bottle = 100 ml; Capacity of large bottle = 1 l = 1000 ml

Step: Number of 100 ml bottles $= \dfrac{1000}{100} = 10$

$$100 \times 10 = 1000\ \text{ml} = 1\ \text{l}$$

$$\boxed{10\ \text{bottles of 100 ml will fill a 1 l bottle.}}$$

Given: $1\ \text{l} = 1000\ \text{ml}$, so $\dfrac{1}{2}\ \text{l} = 500\ \text{ml}$

(i) 250 ml in $\frac{1}{2}$ l (= 500 ml):
$$\frac{500}{250} = \mathbf{2}$$

(ii) 250 ml in 750 ml:
$$\frac{750}{250} = \mathbf{3}$$

(iii) 100 ml in $\frac{1}{2}$ l (= 500 ml):
$$\frac{500}{100} = \mathbf{5}$$

(iv) 100 ml in 800 ml:
$$\frac{800}{100} = \mathbf{8}$$

Concept: Number of 10 ml cups $= \dfrac{\text{Total capacity}}{10\ \text{ml}}$

10 ml to fill 100 ml bottle:
$$\frac{100}{10} = \mathbf{10}\ \text{cups}$$

(a) 10 ml to fill 250 ml glass:
$$\frac{250}{10} = \mathbf{25}\ \text{cups}$$

(b) 10 ml to fill 500 ml vessel:
$$\frac{500}{10} = \mathbf{50}\ \text{cups}$$

(c) 10 ml to fill 1 l (= 1000 ml) bottle:
$$\frac{1000}{10} = \mathbf{100}\ \text{cups}$$

(a) 1 ml droppers to fill a 10 ml dosing cup:
$$\frac{10\ \text{ml}}{1\ \text{ml}} = \mathbf{10}\ \text{droppers}$$

(b) 1 ml droppers to fill a teaspoon:

A standard teaspoon holds approximately 5 ml.
$$\frac{5\ \text{ml}}{1\ \text{ml}} = \mathbf{5}\ \text{droppers}$$

(Students should verify by actually using a dropper and a teaspoon.)

(a) Eye drops: Less than 1 ml at a time (just 1–2 drops, each drop is about 0.05 ml).

(b) Honey: About 5–10 ml (1–2 teaspoons) at a time.

(c) Cough Syrup: About 5–10 ml (1–2 teaspoons) at a time, as prescribed by the doctor.

(d) Cooking Oil: About 10–30 ml (1–3 tablespoons) at a time for cooking one dish.

(Students should check the labels on bottles at home and discuss with parents.)

Given: Total oil = 1 l = 1000 ml

Concept: Number of bottles $= \dfrac{1000\ \text{ml}}{\text{size of each bottle}}$

(a) Ms Shetty — 500 ml bottles:
$$\frac{1000}{500} = \mathbf{2}\ \text{bottles}$$

(b) Mr Muthukumar — 200 ml bottles:
$$\frac{1000}{200} = \mathbf{5}\ \text{bottles}$$

(c) Ms Naini — 100 ml bottles:
$$\frac{1000}{100} = \mathbf{10}\ \text{bottles}$$

(d) Ms Kannan — 50 ml bottles:
$$\frac{1000}{50} = \mathbf{20}\ \text{bottles}$$

Answer (sample — students should measure and fill in their own data):

(Students should use the bottles collected — 500 ml, 250 ml, 100 ml, 50 ml, 10 ml — to measure and fill in the actual capacities.)

Answer (sample):

(Students should visit shops near their home and write the actual items they find in each category.)

(a) Water I drink in a day:
I drink about 6–8 glasses of water per day. Each glass holds about 250 ml.
$$6 \times 250\ \text{ml} = 1500\ \text{ml} = 1.5\ \text{l}$$
I found out by counting the number of glasses I drink each day.

(b) Water a crow can drink at a time:
A crow can drink about 5–10 ml of water at a time (a few sips).

(c) Milk I drink in one day:
I drink about 1–2 glasses of milk per day.
$$1\ \text{glass} \approx 200\ \text{ml}$$
So I drink about 200–400 ml of milk per day.

(d) Water an elephant drinks in a day:
An elephant drinks about 100–200 litres of water in a day. This is a very large amount because elephants are very big animals.

(a) Water for taking a shower:
About 50–100 litres of water is used for a shower.

(b) Watering crops in a field:
A large amount — about thousands of litres per day depending on the size of the field. For example, 1 hectare of crop may need about 5,000–10,000 litres per day.

(c) Watering flowering plants:
About 1–5 litres per plant per day, depending on the size of the plant.

(d) Washing clothes:
About 30–60 litres for washing a full load of clothes by hand; a washing machine uses about 50–100 litres per wash.

(These are approximate values. Students should discuss with their family and compare.)

Activity:

Step 1: Place a container under the leaking tap for 1 hour.

Step 2 (Sample observation): Suppose the container collects 100 ml in 1 hour.

Water lost in 1 hour: $100\ \text{ml}$

Water lost in 1 day (24 hours):
$$100\ \text{ml} \times 24 = 2400\ \text{ml} = 2.4\ \text{l}$$

Water lost in 1 week (7 days):
$$2.4\ \text{l} \times 7 = 16.8\ \text{l}$$

Conclusion: Even a slow drip wastes a large amount of water over time. This shows how important it is to fix leaking taps immediately to conserve water. Water is precious and we must not waste it.