Q&A - P4 Math

[Sun_2010]

BigDevil:

With DD in P4, I'm also interested to find out how to do this \"estimation\".

Just by visually, or have to work out the problem?

In the question posted by cftan,
384 x 23 = 8832
380 x 20 = 7600
400 x 20 = 8000

So the better estimate is 400 x 20 (difference of 832 from actual answer,
as compared to difference of 1232 for 380 x 20).

Just my take, not sure what is being taught ...
If we round up one of the numbers , the other should be rounded down.
Also the bigger number can be rounded up/down more ( times the factor) compared to the smaller number .
Rounding both up or both down could result in a compounded increase or decrease

Like 384 became 400 ie rounded up ( ie add 16 )
So 23 should be rounded down to 20 (ie substract 3).
Dont need to do this but for explanation, roughly
The effect of adding 16 means we have increased the answer by
16 times 23 =300++
The effect of substracting 3 means we have decreased the answer by 3 times 384 = 1100++
The the net diff will be 800+-

another point is the bigger number can be rounded up or down more ( depending on how much bigger it is ) than the smaller number .

Like even though 384 was rounded up to 400 (diff is 16) , its impact is less than the rounding down of 23 to 20 ( diff is 3)

hope I have not confused things :skeptical:

[BigDevil]

Thanks, Sun!

Will remember that when teaching DD.

[Poppet]

A figure has a total of 324 squares.Which figure is that?


Can someone solve this question? :?:

[cftan]

HAPPYH:

BigDevil:

With DD in P4, I'm also interested to find out how to do this \"estimation\".

Just by visually, or have to work out the problem?

In the question posted by cftan,
384 x 23 = 8832
380 x 20 = 7600
400 x 20 = 8000

So the better estimate is 400 x 20 (difference of 832 from actual answer,
as compared to difference of 1232 for 380 x 20).

My goodness. I always tell my DD rounding of to the nearest 10 will be the better estimate. Unless they do proper multiplication, they will not know the correct answer. Really this estimation confusing.

Hi,

I had checked with DS's teacher and was told that the students are not expected to derived an actual answer before they select the correct answer for MCQ. It is a question on estimation. So got to just \"Estimate\" and not \"calculate\". Unless the child is very good is mental calculation else all the workings to derived to an actual answer might takes up too much time.
Just to share the feedback that I got.

[BigDevil]

Did the teacher provide guidelines on how to estimate?

[BigDevil]

Poppet:

A figure has a total of 324 squares.Which figure is that?


Can someone solve this question? :?:

18 x 18 = 324

[Poppet]

Ron and Sharon had the same amount of money.After Ron gave $81 to Sharon, she had thrice as much as Ron.How much more money did Sharon have than Ron in the end?



Can anyone help solve this question?

[iLoveChubby]

Hi Poppet

The only possibility that S can get thrice the amt of R after R gave S $81, is that R is giving S half of what he had.

So after R gave S $81,
R (left) = $81
S (now) = $243 (3x$81)
Difference = $162?

Or a faster way is after establishing e fact that R gave S half of what he had,
R = 1 unit ($81)
S = 3 units
Difference = 2 units = $162

[plum-cake]

Hi,

I need help Please…
Tin Jin saved $3500 in April. His monthly salary is twice the amount he saved in April. He saved $4200 less than the amount he spent in May. How much did he save in May?

from MPH P4 math work book, Part 1 page 53.

TIA

[ponyo]

monthly salary=3500*2=7000

Assume no change in salary,
then in May, amt spent+amt saved=7000

http://i48.tinypic.com/3588e2b.jpg\">


2u->7000-4200=2800
1u->1400

Amt saved in May =1400