Ravi measures a plant and finds it is 45 cm tall. Express this height in metres.

1. 1 metre (m) = 100 centimetre (cm).
2. Height = 45 cm = 45 ÷ 100 m = 0.45 m.

A sample of soil weighs 250 g. Express this mass in kilograms (kg).

1. 1 kg = 1000 g.
2. Mass = 250 g = 250 ÷ 1000 kg = 0.25 kg.

An observation was taken at 2:15 pm and repeated after 90 minutes. What is the new time?

1. 90 minutes = 1 hour 30 minutes.
2. 2:15 pm + 1 hour 30 minutes = 3:45 pm.
3. Answer: 3:45 pm.

A seedling was 4 cm tall on Monday and 9 cm tall on Saturday (5 days later). Calculate the average growth per day.

1. Change in height = 9 cm − 4 cm = 5 cm.
2. Time = 5 days.
3. Average growth per day = 5 cm ÷ 5 days = 1 cm/day.

In a class activity, 18 out of 24 students observed that sugar dissolves faster in hot water. What percentage observed this?

1. Percentage = (part / whole) × 100 = (18 / 24) × 100.
2. (18 ÷ 24) = 0.75 → 0.75 × 100 = 75%.

In an experiment, sugar dissolves in hot water in 30 seconds and in cold water in 90 seconds. How many times faster is dissolving in hot water compared to cold?

1. Rate ∝ 1 / time (faster when time is less).
2. Speed ratio = 90 s ÷ 30 s = 3. So sugar dissolves 3 times faster in hot water.

Three students measured a table length as 120 cm, 118 cm and 122 cm. Find the average (mean) length.

1. Sum = 120 + 118 + 122 = 360 cm.
2. Average = 360 ÷ 3 = 120 cm.

If 4 plants need 8 litres of water per week, how much water do 10 plants need per week (same conditions)?

1. Water per plant = 8 L ÷ 4 = 2 L per plant per week.
2. For 10 plants = 10 × 2 L = 20 L per week.

One beaker contains 0.75 L of solution and another contains 750 mL. Are these volumes equal?

1. 1 L = 1000 mL → 0.75 L = 0.75 × 1000 mL = 750 mL.
2. Yes — both are 750 mL, so they are equal.

A sample had 50 seeds; 40 germinated. What percent germinated and what percent did not?

1. Germinated percent = (40 / 50) × 100 = 80%.
2. Did not germinate = 100% − 80% = 20%.

An observation started at 09:20 and ended at 11:05. How long did the activity run?

1. From 09:20 to 11:05 = 1 hour 45 minutes.
2. Convert to minutes if needed: 1 h 45 min = 60 + 45 = 105 minutes.

In a tray of 30 objects, 12 are smooth and 18 are rough. What is the ratio of smooth to rough?

1. Ratio smooth : rough = 12 : 18. Simplify dividing by 6 → 2 : 3.
2. Answer: 2 : 3.

Three trials of an experiment took 45 s, 50 s and 40 s. What is the average trial time?

1. Sum = 45 + 50 + 40 = 135 s.
2. Average = 135 ÷ 3 = 45 s.

If 5 students observe 3 insects each, how many insects were observed in total? If class has 30 students and each observes same number, total insects?

1. First total = 5 × 3 = 15 insects.
2. If each of 30 students observes 3 insects → 30 × 3 = 90 insects.

A student records an event lasting 2 minutes 20 seconds. Express this duration in seconds.

1. 2 minutes = 2 × 60 s = 120 s. Add 20 s → 120 + 20 = 140 s.

An experiment uses 50 mL of solution for one setup. How much solution is needed for 6 setups?

1. For 6 setups: 50 mL × 6 = 300 mL.

A plant's height increased from 10 cm to 12 cm in one week. What is the percentage increase?

1. Increase = 12 − 10 = 2 cm.
2. Percentage increase = (2 / 10) × 100 = 20%.
3. Answer: 20%.

Convert 7.3 cm into millimetres (mm). (1 cm = 10 mm)

1. 7.3 cm = 7.3 × 10 mm = 73 mm.

A student estimates there are about 475 grains of sugar in a jar. Round this estimate to the nearest hundred.

1. Nearest hundred: 475 → 500 (because tens digit 7 ≥ 5).
2. Answer: 500.

Water is H₂O. If 3 water molecules are written, show correct notation and count of hydrogen and oxygen atoms.

1. 3 molecules of H₂O: write as 3 × H₂O (or H₂O × 3).
2. Each molecule has 2 hydrogen (H) and 1 oxygen (O).
3. Total hydrogen atoms = 3 × 2 = 6 H atoms; oxygen atoms = 3 × 1 = 3 O atoms.