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maths question - speed, distance and time

tg.PNG
I got 19 days instead of 25. What am I doing wrong?

3000 miles
20 m/h

Time = 3000/20 = 150 hours / 8 =18.7... = 19 days
Reply 1
Original post by sqrt of 5
tg.PNG
I got 19 days instead of 25. What am I doing wrong?

3000 miles
20 m/h

Time = 3000/20 = 150 hours / 8 =18.7... = 19 days

It makes more sense to round 15.12 to 15 instead of 20 since 3000/15 is easy. I don't know if you're following the rule "always round to 1sf" but this rule should not be followed and you should instead think what the best estimation should be for every question.

It's possible you would have got some/all of the marks in the real exam. Was this from a real exam paper?
Reply 2
Round 15.12 to 15 and not 20. Then find the distance traveled per day from s=d/t and divide 3000 by that to give the number of days it would take.
(edited 5 years ago)
Reply 3
Original post by Notnek
It makes more sense to round 15.12 to 15 instead of 20 since 3000/15 is easy. I don't know if you're following the rule "always round to 1sf" but this rule should not be followed and you should instead think what the best estimation should be for every question.

It's possible you would have got some/all of the marks in the real exam. Was this from a real exam paper?


yes i am and for this reason i think that the mark scheme allows this answer as well (?)
Reply 4
Original post by sqrt of 5
yes i am and for this reason i think that the mark scheme allows this answer as well (?)

There's a chance that you wouldn't get full marks for that.

As long as your estimate is appropriate then you should get the marks but it's hard to say whether rounding 15.12 to 20 is appropriate in the eyes of examiners.
(edited 5 years ago)
Original post by Notnek
There's a chance that you wouldn't get full marks for that.

I don't know why loads of students follow the "1sf rule" but it is not in any of the 9-1 specs so you should not follow it. As long as your estimate is appropriate then you should get the marks but it's hard to say whether rounding 15.12 to 20 is appropriate in the eyes of examiners.


See the following from examiner's report & exemplars.
This question is from June18 Foundation Paper 1 (Edexcel), and also used on Higher Paper 1 (q4). Both papers are non-calc.

Notes to MS also allowed for '8' to be rounded to 10 . [ ie 1 sig fig.]

there was a range of solutions which were allowed full marks, and part b allowed for any appropriate rounding used in part a.

My opinion : an unfortunate choice of numbers for this type of question (made it a nightmare to mark). Clarification is needed on whether rounding to 1 sig fig is supported.
Reply 6
Original post by begbie68
See the following from examiner's report & exemplars.
This question is from June18 Foundation Paper 1 (Edexcel), and also used on Higher Paper 1 (q4). Both papers are non-calc.

Notes to MS also allowed for '8' to be rounded to 10 . [ ie 1 sig fig.]

there was a range of solutions which were allowed full marks, and part b allowed for any appropriate rounding used in part a.

My opinion : an unfortunate choice of numbers for this type of question (made it a nightmare to mark). Clarification is needed on whether rounding to 1 sig fig is supported.

Thank you, I thought I recognised this question!

I kind of wish that 20 wasn't allowed because there's no need to estimate to 20 and you lose loads of accuracy. I don't know why people follow the 1sf rule because in real life you make sensible choices instead of using a fixed method.
Original post by Notnek
Thank you, I thought I recognised this question!

I kind of wish that 20 wasn't allowed because there's no need to estimate to 20 and you lose loads of accuracy. I don't know why people follow the 1sf rule because in real life you make sensible choices instead of using a fixed method.


I agree, but it just sort of became a rule at GCSE. Then teachers started preaching this 'rule' and it stuck. Sadly.

I'm fairly sure that there are some past questions where 'sensible' rounding which wasn't to 1 sig fig was marked as wrong. Wrongly. IMO, of course!!

It's similar to rationalising the denominator. I never saw such a thing when I was at school / Uni (ok, it was a long time ago ...) , and then it sort of became a 'thing' , -certainly at GCSE/GCE ... but at Further Maths, we can ignore it again ...
Reply 8
Original post by begbie68
I agree, but it just sort of became a rule at GCSE. Then teachers started preaching this 'rule' and it stuck. Sadly.

I'm fairly sure that there are some past questions where 'sensible' rounding which wasn't to 1 sig fig was marked as wrong. Wrongly. IMO, of course!!

It's similar to rationalising the denominator. I never saw such a thing when I was at school / Uni (ok, it was a long time ago ...) , and then it sort of became a 'thing' , -certainly at GCSE/GCE ... but at Further Maths, we can ignore it again ...

In the new spec the exam boards should have clarified that estimations may not always be 1sf. I've always taught students to estimate sensibly - I don't care what other teachers preach.

If a primary school student was asked to estimate 45/5.023 then they would say 9. It's ridiculous that GCSE students are taught that they should estimate this to 10 :grumble:
Reply 9
Original post by begbie68
See the following from examiner's report & exemplars.
This question is from June18 Foundation Paper 1 (Edexcel), and also used on Higher Paper 1 (q4). Both papers are non-calc.

Notes to MS also allowed for '8' to be rounded to 10 . [ ie 1 sig fig.]

there was a range of solutions which were allowed full marks, and part b allowed for any appropriate rounding used in part a.

My opinion : an unfortunate choice of numbers for this type of question (made it a nightmare to mark). Clarification is needed on whether rounding to 1 sig fig is supported.


Phew! Where did you find the examiner's report?

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