Video: KS2-M18 • Paper 2 • Question 19

Layla wants to estimate the answer to this calculation (3 9/20) − (2 1/8) + (1 4/5.) Tick the calculation that is the best estimate. [A] 3 − 2 + 2 [B] 4 − 2 + 1 [C] 4 − 2 + 2 [D] 3 − 2 + 1

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Video Transcript

Layla wants to estimate the answer to this calculation. Three and nine twentieths subtract two and one-eighth plus one and four-fifths. Tick the calculation that is the best estimate. Three take away two plus two, four take away two plus one, four take away two plus two, or three take away two plus one.

The question is asking us to estimate three and nine twentieths subtract two and an eighth plus one and four-fifths. Three and nine twentieths comes between three and four on the number line. If we divide this line into 20 equal parts, by marking on 20 divisions, this will help us to mark three and nine twentieths onto the number line.

To help us estimate, we need to round this number to the nearest whole number. Three and nine twentieths is nearest to three. Two and one-eighth comes between two and three on the number line. We’ve divided the number line into eight equal parts or divisions. And each division is worth an eighth. This is where two and one-eighth would go on the number line. So we can see that its nearest whole number is two. One and four-fifths is between one and two on the number line. Each division is worth one-fifth, and the nearest whole number is two.

We can estimate three and nine twentieths subtract two and one-eighth plus one and four-fifths to be three subtract two plus two. This is the calculation which is the best estimate. So this is the calculation that we need to tick.