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Estimation

zed963

How would I estimate this

(410*6.9)/(0.23)

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Reply 1

claret_n_blue

Maybe multiply everything by 100 so you have

(41,000 * 690)/23

Then work that out, then divide the answer by 100?

Reply 2

Hasufel

you can prime factorise it as: (2x2x2x3x5x5x5x23x41)/(2x5x23) = 10x10x3x41... =100 x 123

(from: 410 = 2x5x41), 6.9 = 69/10 = (3x23)/(2x5), and divided by .23 = x100/23 = (2x2x5x5/23)

(edited 11 years ago)

Reply 3

zed963

Original post by SubAtomic

You would round the 6.9 to 7 the 0.23 to 0.2

So you'd have

\displaystyle\frac{410 \times 7}{0.2}

Its in a non calculator exam.

How would I do it without using a calculator

Reply 4

TenOfThem

Original post by zed963

How would I estimate this

(410*6.9)/(0.23)

I would round to 400, 7, and 0.25

2800*4 = 11200

(edited 11 years ago)

Reply 5

Repressor

The /0.2 is the same as *5 on the top. Also, I'm pretty sure when estimating you have to round all numbers to 1s.f.

So you'd end up with

400*7*5

2000*7= 14000

Reply 6

usycool1

Original post by zed963

Its in a non calculator exam.

How would I do it without using a calculator

Do 410 x 7 (it isn't such a hard multiplication sum to do without a calculator)
Multiply by 5 (as dividing by 0.2 is basically the same as multiplying by 5)

:smile:

Reply 7

zed963

Original post by Repressor

The /0.2 is the same as *5 on the top. Also, I'm pretty sure when estimating you have to round all numbers to 1s.f.

So you'd end up with

400*7*5

2000*7= 14000

Perfect that was the answer

Reply 8

Hasufel

perfect - if you don`t mind being 1700 out! (what kind of an estimate does someone [a teacher?] consider THAT?)

(edited 11 years ago)

Reply 9

zed963

Original post by Hasufel

perfect - if you don`t mind being 1700 out! (what kind of an estimate does someone [a teacher?] consider THAT?)

The screen shot above is from a multiple choice paper.

There are only five or so options there to choose from and it has to be A

I know its 1700 or so off but it is an estimation not an exact thing.

Haterz gonna hate :P

(edited 11 years ago)

Reply 10

raheem94

Original post by zed963

I can't see a screen shot.

Can you post a screen shot of the question.

Original post by SubAtomic

\displaystyle\frac{40 \times 7 + 1 \times 7 \ \ \mathrm{add\ a\ 0\ on}}{.2}

Raise top and bottom by 5 to get

\displaystyle 2870 \times 5 =14350

I am just guessing that this question may not require a calculation. zed963 says that its a multiple choice question, so in that they may have given options that are very far from each other, so by looking at the question and doing a rough calculation in your head the answer can be deduced.

(edited 11 years ago)

Reply 11

username650017

Original post by TenOfThem

I would round to 400, 7, and 0.25

2800*4 = 11200

I would round it in exactly the same way. :tongue:

Why NEG rep??? :mad:

(edited 11 years ago)

Reply 12

raheem94

Original post by SubAtomic

How more rough can one get than that.

Maybe at GCSE a bit of working/scribbling is needed to be sure.

By rough i meant that 5*400*7 can be easily done in head.

It hardly takes 5-10 second to calculate this in your mind. And the answer choices given will probably have values which are a lot far from each other.

Reply 13

raheem94

Original post by SubAtomic

Depends on whos head :holmes:

A person doesn't needs to be Scott Flansburg to do this simple calculation.

Anyone can do this barring some mathematical exceptions.

Reply 14

raheem94

Original post by SubAtomic

Not saying they do but what is simple to you or me is not simple to others and vice versa.

Fair enough.

Though it isn't very difficult to find the exact value of this as well, here's how i will find its exact value

\displaystyle \frac{410 \times 6.9}{0.23} = \frac{410 \times 6.9}{\frac{23}{100}} = \frac{410 \times 690}{23} = \frac{410 \times 3 \times 23 \times 10 }{23} = 410 \times 3 \times 10 \\ = 4100 \times 3 = 12300

It is so easy to calculate its exact value, though it requires some working.

Reply 15

raheem94

Original post by Hasufel

you can prime factorise it as: (2x2x2x3x5x5x5x23x41)/(2x5x23) = 10x10x3x41... =100 x 123

(from: 410 = 2x5x41), 6.9 = 69/10 = (3x23)/(2x5), and divided by .23 = x100/23 = (2x2x5x5/23)

Look at my method to find the exact value of this.

NB: I didn't gave you the neg rep.

Reply 16

raheem94

Original post by SubAtomic

Yes I know it is easy for us to calculate the exact value, not debating that but now zed has a lot to look at and learn from :biggrin:

zed is GCSE(I think) we are A-level.

Zed is a year 10 student hoping for an A* in GCSE maths.

I just wanted to give a better method of calculating the exact value, i wasn't impressed by Hasufel's method, i really don't understand how does he expects zed to understand his method.

Reply 17

cyfer

Original post by zed963

How would I estimate this

(410*6.9)/(0.23)

I'd estimate by doing

400*7=2800
2800/0.2=2800*5=14000

Reply 18

raheem94

Original post by SubAtomic

Has Zed purchased any GCSE books yet?

This question can only be answered by Zed.

The book I worked through when I did mine explained what level of accuracy to use when rounding numbers so all us on here are guessing other than a GCSE teacher.