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# Calculator and issues with decimals watch

1. I've been going through past papers doing questions and I've noticed that if I do each step manually, I get an answer that's a little off and not accepted in the mark scheme.

Example 1
Here is a list of the ingredients needed to make lentil soup for 6 people. Lentil Soup (for 6 people) 120 g lentils 300 g carrots 800 ml vegetable stock 3 onions Jenny wants to make lentil soup for 24 people.

So if I do 800/6, that gives me 133.3ml. Then doing 133.3x24, it gives me 3199.2.

According the the mark scheme, the answer is actually 3200 and 3199.2 won't be accepted.

Example 2
Lizzy drove by car to visit her aunt. She left home at 930 am. Lizzy arrived at her aunt’s house at 1115 am. She drove a distance of 140 km. Work out, in km/h, Lizzy’s average speed for the journey.

I did 140/105 which gives me 1.3km/min, so 60x1.3 is 78mph. But if I do 140/105x60, I get 80. 80 is the only answer the scheme accepts.

So what's going on and is there a way to fix this problem with the FX-83GT Plus? Or do I have to remember to do it all in one calculation?
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2. (Original post by LeiPoorGuyAh)
I've been going through past papers doing questions and I've noticed that if I do each step manually, I get an answer that's a little off and not accepted in the mark scheme.

Example 1
Here is a list of the ingredients needed to make lentil soup for 6 people. Lentil Soup (for 6 people) 120 g lentils 300 g carrots 800 ml vegetable stock 3 onions Jenny wants to make lentil soup for 24 people.

So if I do 800/6, that gives me 133.3ml. Then doing 133.3x24, it gives me 3199.2.

According the the mark scheme, the answer is actually 3200 and 3199.2 won't be accepted.

Example 2
Lizzy drove by car to visit her aunt. She left home at 930 am. Lizzy arrived at her aunt’s house at 1115 am. She drove a distance of 140 km. Work out, in km/h, Lizzy’s average speed for the journey.

I did 140/105 which gives me 1.3km/min, so 60x1.3 is 78mph. But if I do 140/105x60, I get 80. 80 is the only answer the scheme accepts.

So what's going on and is there a way to fix this problem with the FX-83GT Plus? Or do I have to remember to do it all in one calculation?
The first one you can just multiply by four, so they are penalising you for adding an unnecessary step which seems reasonable.
3. (Original post by LeiPoorGuyAh)
I've been going through past papers doing questions and I've noticed that if I do each step manually, I get an answer that's a little off and not accepted in the mark scheme.

Example 1
Here is a list of the ingredients needed to make lentil soup for 6 people. Lentil Soup (for 6 people) 120 g lentils 300 g carrots 800 ml vegetable stock 3 onions Jenny wants to make lentil soup for 24 people.

So if I do 800/6, that gives me 133.3ml. Then doing 133.3x24, it gives me 3199.2.

According the the mark scheme, the answer is actually 3200 and 3199.2 won't be accepted.

Example 2
Lizzy drove by car to visit her aunt. She left home at 930 am. Lizzy arrived at her aunt’s house at 1115 am. She drove a distance of 140 km. Work out, in km/h, Lizzy’s average speed for the journey.

I did 140/105 which gives me 1.3km/min, so 60x1.3 is 78mph. But if I do 140/105x60, I get 80. 80 is the only answer the scheme accepts.

So what's going on and is there a way to fix this problem with the FX-83GT Plus? Or do I have to remember to do it all in one calculation?
Your answer is to the wrong number of significant figures. You should always round your answer to the same number of significant figures as the value in the question with the least number of significant figures. In question one, this is two significant figures. 3199.2 rounded to 2 significant figures is 3200

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4. (Original post by Kyx)
Your answer is to the wrong number of significant figures. You should always round your answer to the same number of significant figures as the value in the question with the least number of significant figures. In question one, this is two significant figures. 3199.2 rounded to 2 significant figures is 3200

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Will keep in mind, thanks!
5. (Original post by LeiPoorGuyAh)
Will keep in mind, thanks!
Just to add to this, where possible use algebra for as long as you can and do all of the calculations in one sum rather than step by step - and don't round until the end. Otherwise you're likely to make rounding errors at some point ☺

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6. (Original post by LeiPoorGuyAh)
I've been going through past papers doing questions and I've noticed that if I do each step manually, I get an answer that's a little off and not accepted in the mark scheme.

Example 1
Here is a list of the ingredients needed to make lentil soup for 6 people. Lentil Soup (for 6 people) 120 g lentils 300 g carrots 800 ml vegetable stock 3 onions Jenny wants to make lentil soup for 24 people.

So if I do 800/6, that gives me 133.3ml. Then doing 133.3x24, it gives me 3199.2.

According the the mark scheme, the answer is actually 3200 and 3199.2 won't be accepted.

Example 2
Lizzy drove by car to visit her aunt. She left home at 930 am. Lizzy arrived at her aunt’s house at 1115 am. She drove a distance of 140 km. Work out, in km/h, Lizzy’s average speed for the journey.

I did 140/105 which gives me 1.3km/min, so 60x1.3 is 78mph. But if I do 140/105x60, I get 80. 80 is the only answer the scheme accepts.

So what's going on and is there a way to fix this problem with the FX-83GT Plus? Or do I have to remember to do it all in one calculation?
I assume that, at the moment, you are entering your halfway answer back into the calculator. Don't!

For the first one, do 800/6. Your calculator now says 133.333333333

Don't clear it, just type x 24. It will give you 3200 for your answer.
7. (Original post by tiny hobbit)
I assume that, at the moment, you are entering your halfway answer back into the calculator. Don't!

For the first one, do 800/6. Your calculator now says 133.333333333

Don't clear it, just type x 24. It will give you 3200 for your answer.
Better yet, type (800*24)/6 in the first place

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8. (Original post by Implication)
Better yet, type (800*24)/6 in the first place

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Not better, just the same! (and the OP has to worry about whether brackets are needed)
9. (Original post by tiny hobbit)
Not better, just the same! (and the OP has to worry about whether brackets are needed)
Probably the same functionally for most sensible calculators, but the potential for human error is substantially lower. Particularly if OP ever has to deal with calculations involving more than 2 or 3 quantities, which is almost guaranteed to be the case if they go on to study in higher education!

Working out where to place the brackets is exactly the same as working out the order in which to perform the calculations

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