Talk

How do you round decimal figures?

(49 Posts)
cakedup Sat 28-Oct-17 22:35:37

So how would you round, to one one significant figure, 0.46 for example? Because we've tried 0.5, 0, and 1 and none of them seem to be right!

PerspicaciaTick Sat 28-Oct-17 22:40:48

0.5

it depends on the format of the question. How many decimal places is it asking for?

Rounding to a whole number would be 1. To 1 decimal place would be 0.5 etc

DumbledoresApprentice Sat 28-Oct-17 22:48:23

Rounding to a whole number would be 0 surely?

DumbledoresApprentice Sat 28-Oct-17 22:51:38

I think that 0.5 would be one significant figure though. Either way I’m stumped if it’s definitely not 0 or 0.5

Mxyzptlk Sat 28-Oct-17 22:51:42
EasterRobin Sat 28-Oct-17 22:52:28

To one significant figure would be 0.5

Damia Sat 28-Oct-17 23:07:48

With significant figures I think it needs to be the same number of digits in total as the original so 0.50 not just 0.5

JustRichmal Sun 29-Oct-17 09:12:19

It should be 0.5 as 0.50 suggests the accuracy is to 2 decimal places.

cakedup Sun 29-Oct-17 10:02:42

The question is:
By rounding each number to 1 significant figure, estimate the answer to:
8.2 x 6.7 divided by 0.46

So we've done it like this:

8 x 7 = 56
60 ÷ 0.5 = 120

But it's incorrect! (online instant marking)

LetsSplashMummy Sun 29-Oct-17 10:07:44

Perhaps don't round up the in between step, from 56 to 60, I'd say that was more open to interpretation than 0.46 becoming 0.5.

Ifailed Sun 29-Oct-17 10:08:17

Dermymc Sun 29-Oct-17 10:08:59

Yes don't round the 56, it should be 56/0.5 which is 112.

Ifailed Sun 29-Oct-17 10:10:18

Both 112 and 120 to 1 sf are 100.

MsMarvel Sun 29-Oct-17 10:10:20

Yeah I dont think 56 needs to be rounded.

ProfessorCat Sun 29-Oct-17 10:10:42

6.7 might round to 6.5

SandLand Sun 29-Oct-17 10:17:09

I'd round each of the numbers, then calculate without further rounding.
So 8*7÷0.5=112

moomoo222 Sun 29-Oct-17 10:21:10

I would calculate it as 112 as PP's have done, does that work!?

PickleFish Sun 29-Oct-17 10:38:52

yes it doesn't say to round the answer, only the numbers in the question, so I'd try 112 as well.

cakedup Sun 29-Oct-17 10:44:47

Yes, it's 112! Weird really, I would have thought you kept on going with the rounding off, it does say 'estimate' the answer and 112 doesn't sound like an estimate

cakedup Sun 29-Oct-17 10:45:55

Erm....so how would you round 0.18 to a significant figure? Would that be 0 then??

SandLand Sun 29-Oct-17 10:48:14

One Sig fig? 0.2

noblegiraffe Sun 29-Oct-17 10:50:45

0.18 to 1 sig fig is 0.2.

With estimation questions in maths, the official GCSE ‘procedure’ is to round each number in the calculation to 1 sig fig and then do it in your head. You wouldn’t round interim figures, so you’d do 56/0.5 which is just doubling.

SandLand Sun 29-Oct-17 10:50:53

And 0.018 would go to 0.02.
0.0018 would go to 0.002

cakedup Sun 29-Oct-17 10:54:15

Ok, last one i promise, to get my head around this.

So 23.4 x 13.9 divided by 0.18

So wouldn't that be:
23 x 14 = 322
322 ÷ 0.2 = 1610

Apparently not! What am I getting wrong??

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