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Estimation

Maths: Edexcel IGCSE Higher, topic 1.8.2

Estimations

We can make estimations by rounding numbers before we do calculations.

E.g.1: This is hard to do in your head

E.g.1: This is hard to do in your head

E.g.1: So we round 4.95 to 1

E.g.1: So we round 4.95 to 1

E.g.1: Overestimate

E.g.1: Overestimate

  • This answer is an overestimate because we rounded up before multiplying.
E.g.2: This is hard to do in your head

E.g.2: This is hard to do in your head

E.g.2: So we round 6.03 to 1 significant figure

E.g.2: So we round 6.03 to 1 significant figure

E.g.2: Underestimate

E.g.2: Underestimate

  • This answer is an underestimate because we rounded down before multiplying.

Test yourself on Estimation

  • Lukas wants to go on holiday with his friends. They need to buy 5 plane tickets which each cost £101.83.
    (a) Estimate how much their plane tickets cost.

    (b) Lukas and his friends have exactly £500, can they afford the tickets?

  • Stephen wants to go away for the weekend with his parents. He needs to buy 3 train tickets which each cost £49.99.
    (a) Estimate how much the train tickets cost in total.

    (b) Stephen has exactly £150, can he afford the tickets?

  • William needs 4 sections of rope for a tug of war competition. Each rope needs to be 4.8 m long.
    (a) Estimate how much rope is needed in total.
    (b) Rope is sold in the shop at a length of 20 m, will this be enough?

  • You are trying to do £0.99 x £198 in your head. If you estimate and do £1.00 x £200, will this be an underestimate or an overestimate?

  • You are trying to do £103 x £200 in your head. If you estimate and do £100 x £200, will this be an underestimate or an overestimate?

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