##### Jan Kwok
Asked 7 years ago

SG chevron_right Secondary 3 chevron_right Geometry and Measurement

Could someone teach me how to answer this question without calculator?

Replies 4

4 years ago

4 years ago

Thank you both

4 years ago

4 years ago

##### Irin Oh
Asked 7 years ago

SG chevron_right Primary 2 chevron_right Number and Algebra

Replies 7

##### Yueh Mei Liu

Obj of 1b is to see if student is able to recognise that 335 is 10 less than 345 and that 133 is 10 more than 123, hence the answer will be the same as 1a, without having to calculate.

4 years ago
##### Yueh Mei Liu

Similarly for 2b, obj is for student to recognise that 809 is 100 more than 709 and 353 is 100 more than 253, hence the extra 100 minus itself and it's the same as 709 - 253.

4 years ago
##### BA Poh Ann

If i tutor my tutees to have a better understanding for such qn, I'll use smaller numbers to explain. For example: 12 + 10 = 22 7 + 15 = 22 -- Why? from 12 became 7 (Take away 5) from 10 became 22 (Add 5) When u add snd take away with the same amount, the total remains unchanged. :)

4 years ago
##### BA Poh Ann

error: from 10 became 15. :)

4 years ago

4 years ago
##### Yueh Mei Liu

It's recognising tens and hundreds. So parallel egs should be in tens and hundreds, counting and calculation is not needed.

4 years ago
##### Karen Berlanga

A visual that could help is pulling out place value blocks or discs and putting the addends in each of their own pile (one pile with 345 and one with 123). Then ask the student to find the total sum. Now move ten from one pile (345 now becomes 335) to the other pile (123 now becomes 133). Ask if there is still the same total. Yes! you just moved ten from one number to the next. Have student write the new problem represented by the new piles (335+133= 468) and they'll see they are equal.

4 years ago

##### Winnie Win
Asked 7 years ago

SG chevron_right Primary 6 chevron_right Measurement

Replies 5

##### Gerald Goh

The diameter of semicircle BOC can be derived using the Area of Square = Area of 2 Triangle ABC. Diameter = square root 50

4 years ago
##### Winnie Win

Thanks Gerald Goh. My dd hasn't learnt sq root yet and calculator not allowed. My ans got decimal.

4 years ago
##### Gerald Goh

Is this a P5 question?

4 years ago

P6

4 years ago
##### Pieter Cronje

Sqroot of 50 is very close to 49...so i suggest using 7 .

4 years ago

##### Elsie Tan
Asked 7 years ago

SG chevron_right chevron_right

Thanks for accepting.

Replies 0

##### Philip Chua
Asked 7 years ago

SG chevron_right chevron_right

Dear All, I have a problem with this question and do not know how to solve it. Can someone help, please?? Thank you.

Replies 3

##### Soo Vei Li

385 = 5 x 7 x 11. These prime factors can be used to form the L and B of rectangles (385 is the area of the rectangle) 35 x 11, 5 x 77 and 55 x 7. And there is also 1 x 385. So there are 4 ways.

4 years ago
##### Jojo Celestino

basically, the 385 identical squares can be considered as tiles that you need to put together in order to form rectangles. since you need to use all 385 tiles to make a rectangle, you can say that the area of your rectangle must be 385 square units.. now that you know the rectangle's area, the thing left for you to do is identify the different dimensions that will give an area of 385 square units.. there can be more than one set of dimensions that can satisfy this requirement.. Here are the possible sets of dimensions: length = 1 unit breadth = 385 units area = 385 square units length = 5 units breadth = 77 units area = 385 square units length = 7 units breadth = 55 units area = 385 square units length = 11 units breadth = 35 units area = 385 square units Since you can only come up with 4 sets, that means you can have 4 different rectangles.. This problem combines the concepts of area of a rectangle and factors.. The specific heuristics that can be used are guess&check and making a systematic list.. Hope this helps! :)

4 years ago
##### Philip Chua

Hi Jojo and Vei Li, Thank you for your help.

4 years ago