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1.3 Decimals — Worksheet

Quick Notes & Formulae

Core rules and reminders for decimals.

Conversions
Multiply by 100 for %, divide by 100 for decimals. Simplify fractions.
Ordering
Pad zeros so digits align: 0.5=0.500 for comparison.
Add/Subtract
Always line up decimal points before operating.
Multiply
Ignore decimals, multiply, then place total decimal places in the result.
Divide
Shift both numbers to make the divisor a whole number.
Rounding
To n d.p., use half-unit 0.5×10−n for bounds.

Past Paper Style Questions

Q1: Fraction–decimal–percentage conversions

(a) Write 0.36 as a fraction in its simplest form.
(b) Convert 720 to a decimal.
(c) Convert 0.075 to a percentage.
(d) Convert 62.5% to a fraction in its simplest form.
(e) Arrange 720,0.36,37% in ascending order.

Q2: Operations with decimals (calculator-style accuracy)

Work out.
(a) 8.47+19.6+0.085
(b) 34.2−7.968
(c) 0.48×3.75
(d) 12.6÷0.35
(e) Round your answer to (d) to 3 significant figures.

Q3: Ordering decimals on a number line

The numbers are: 0.503,0.53,0.509,0.5003,0.505
(a) Write them in ascending order.
(b) State the smallest and the largest number.
(c) Which number is closest to 0.51? Show a subtraction to justify.
(d) Write down one number from the list that lies between 0.504 and 0.508.

Q4: Rounding to decimal places and significant figures

A length is 18.3765 cm.
(a) Round the length to 1 decimal place.
(b) Round the length to 3 decimal places.
(c) Round the length to 3 significant figures.
(d) State the value of the rounding error when the length is rounded to 1 decimal place.
(e) Write the upper and lower bounds for the length when rounded to 1 decimal place.

Q5: Reverse rounding (place value reasoning)

A number N is rounded to 2 decimal places and the result is 6.48.
(a) Write the smallest possible value of N.
(b) Write the greatest possible value of N.
(c) Write your answers to (a) and (b) as inequalities for N.
(d) If N is also rounded to 3 significant figures and gives 6.48, explain whether this gives any new information.

Q6: Percentage change with decimals (context)

A shop reduces the price of a jacket from ₹2499.50 to ₹2149.60.
(a) Find the decrease in price.
(b) Calculate the percentage decrease, correct to 1 decimal place.
(c) The shop then adds 18% GST to the reduced price. Find the final price.
(d) Round the final price to the nearest rupee.
(e) Explain why rounding should be done at the end in this question.

Q7: Reverse algebra with decimals

A decimal x satisfies:
3.2x−1.76=5.92
(a) Solve for x.
(b) Check your answer by substitution.
(c) Write x as a fraction in its simplest form.
(d) Convert your fraction to a percentage.

Q8: Decimals in ratio/proportion

A recipe uses flour, sugar and butter in the ratio 2:1.5:0.8.
(a) Find the total number of ratio parts.
(b) If the recipe uses 600 g of flour, find the mass of sugar.
(c) Find the mass of butter.
(d) Find the total mass of the mixture in kg, correct to 2 decimal places.
(e) What percentage of the mixture is butter? Give your answer to 1 decimal place.

Q9: Reverse rounding with two numbers

Two numbers a and b are decimals.
When a is rounded to 1 decimal place it becomes 4.7.
When b is rounded to 2 decimal places it becomes 1.25.
(a) Write inequalities showing the possible values of a.
(b) Write inequalities showing the possible values of b.
(c) Find the smallest possible value of a+b.
(d) Find the greatest possible value of a−b.
(e) Give your answers to (c) and (d) correct to 2 decimal places.

Q10: Money arithmetic + rounding

A taxi fare is calculated as:
• fixed charge ₹62.50
• plus ₹14.75 per km travelled
A journey is 8.6 km.
(a) Write an expression for the total fare F.
(b) Calculate F.
(c) The driver rounds the fare to the nearest ₹1. What is the amount charged?
(d) A passenger pays with ₹200. Find the change.
(e) Reverse: Another passenger was charged ₹190 (after rounding). Find the possible distance travelled, giving your answer as an interval in km.

Q11: Conversions + ordering

(a) Convert 0.084 to a percentage.
(b) Convert 37.5% to a decimal.
(c) Convert 2150 to a decimal and to a percentage.
(d) Arrange 0.084,37.5%,2150 in ascending order.
(e) Write the largest of the three as a fraction in simplest form.

Q12: Decimal operations (mixed difficulty)

Work out.
(a) 13.08+2.907+0.56
(b) 45.2−17.385
(c) 0.072×35
(d) 6.84÷0.12
(e) Round your answer to (d) to 3 significant figures.

Q13: Ordering on a number line (close decimals)

The numbers are: 2.03,2.3,2.003,2.300,2.13
(a) Write the numbers in ascending order.
(b) Which two numbers are equal? Explain.
(c) Write down the number closest to 2.10. Show your method using subtraction.
(d) Write one number from the list that lies between 2.02 and 2.04.
(e) State the value of 2.3−2.03.

Q14: Rounding (dp vs sf) + error

A mass is 0.004863 kg.
(a) Round the mass to 5 decimal places.
(b) Round the mass to 2 significant figures.
(c) Write the mass in grams, correct to 1 decimal place.
(d) State the rounding error when the mass is rounded to 2 significant figures.
(e) Give the lower and upper bounds for the mass (in kg) when rounded to 2 significant figures.

Q15: Reverse bounds from rounding to 2 d.p.

A value x rounds to 3.47 correct to 2 decimal places.
(a) Write the inequality showing all possible values of x.
(b) State the smallest possible value of x.
(c) State the greatest possible value of x.
(d) Hence find the smallest possible value of 5x.
(e) Hence find the greatest possible value of 5x.

Q16: Reverse solve for a decimal (equation)

A decimal x satisfies
0.6x+1.35=4.71
(a) Solve for x.
(b) Check your answer by substitution.
(c) Write x as a fraction in simplest form.
(d) Write x as a percentage.
(e) Round x to 3 significant figures.

Q17: Money + percentages + rounding

A phone costs ₹18 499. In a sale it is reduced by 12.5%.
(a) Find the amount of the reduction.
(b) Find the sale price.
(c) GST of 18% is added to the sale price. Find the final price.
(d) Round the final price to the nearest rupee.
(e) The customer pays ₹20 000. Find the change.

Q18: Reverse missing decimal using rounding

When a number n is rounded to 1 decimal place it becomes 7.2.
(a) Write an inequality for the possible values of n.
(b) If n is rounded to the nearest whole number it becomes 7, write an inequality for n.
(c) Hence find the possible values of n that satisfy both (a) and (b).
(d) Write the smallest and greatest possible values of n.
(e) Find the range of possible values of n.

Q19: Decimal division + reverse check

(a) Calculate 9.72÷0.36.
(b) Without using a calculator, explain why your answer in (a) must be greater than 20.
(c) Round your answer in (a) to 2 decimal places.
(d) Reverse: Find a number k such that 0.36×k=9.72.
(e) Use (d) to check (a).

Q20: Challenge inequality + context

A tank holds x litres of water. After a leak, it loses 0.75 litres every hour.
After 6 hours, it contains 12.4 litres.
(a) Write an equation in x.
(b) Solve for x.
(c) The initial reading x was recorded correct to 1 decimal place. Write the bounds for x.
(d) Hence write the bounds for the amount of water after 6 hours.
(e) Give your final bounds in (d) correct to 2 decimal places.