Q&A - P4 Math

[cathycho]

Can someone help me on these?


1. 50 is the estimated quotient when a 3 digit number is divided by a 1 digit number. Think of two possible numbers that can give this quotient. The. Check if your answer is correct.

2. A 3 digit number when rounded off to the nearest ten and the nearest hundred will produc the same answer. What is the number?

[meatloaf]

Hi


Can someone help me?

Rashid made 120 more buns than Sam. After Rashid sold 57 buns and Sam sold 105 buns, Rashid had 4 times as many buns as Sam. How many buns did Sam have at first?

Many THanks!

[tianzhu]

meatloaf:

Hi


Can someone help me?

Rashid made 120 more buns than Sam. After Rashid sold 57 buns and Sam sold 105 buns, Rashid had 4 times as many buns as Sam. How many buns did Sam have at first?

Many THanks!

Hi

Hope this helps.

Best wishes

http://farm9.staticflickr.com/8187/8440091606_321a0008c6_z.jpg\">

[cftan]

Hi,


Pls help to advice.

Which of the following is the best estimate for 384 x 23?
(1) 380 x 20
(2) 400 x 20

Ans is (2). Isn’t (1) a closer estimate?

Thanks.

[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).

[cftan]

The topic on "estimation" is a bit tricky for me.


Estimate 1894 / 5

I thought the nearest would be 1890 / 5 but the answer is 2000 / 5.

Can someone advise. Many thanks.

[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.

[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? :?: