Estimation Flashcards

All 6 cards in this deck

True or false? To estimate the answer to a calculation you should work it out exactly and then round the answer.

False. You must round each value to 1 significant figure first; finding the exact answer scores no marks.

What are the steps to use approximation to check whether a given answer is reasonable?
e.g. is $\frac{595}{4.08 \times 5.32}$ equal to $27.1115$ or $271.115$?

1. Round each value to 1 sf: $600$, $4$, $5$
2. Work out the estimate: $600 \div 20 = 30$
3. Compare: $27.1115$ is closest, so that answer is correct

What are the steps to estimate a total cost and say whether it is an under- or overestimate?
e.g. 35 T-shirts costing £$4.85$ each

1. Round each value to 1 sf: $40$ and £$5$
2. Multiply: $40 \times 5 =$ £$200$
3. Both values were rounded up, so it is an overestimate — the real cost is less

In an estimated division, the top number is rounded up and the bottom number is rounded down. Is the estimate an underestimate or an overestimate?

An overestimate — you are dividing a larger number by a smaller number.

What are the steps to estimate a real length from a photograph using a known reference?

e.g. a man stands next to a door, and in the photo he is about three quarters as tall as the door

1. Pick an object whose real size you know: a door is about $2$ m tall.
2. Compare the unknown with it in the picture: the man is about $\frac{3}{4}$ of the door.
3. Multiply: $\frac{3}{4} \times 2 = 1.5$ m.

When estimating sizes in a picture, what real height is used for an adult person as a reference?

About $1.8$ m (any estimate from $1.5$ m to $2$ m is sensible).