Q&A - P5 Math

[speedmaths.com]

Hi, I have doubts on the answer for this question:

A machine takes 60 seconds to cut an iron rod into 6 equal parts, At this rate, how long will it take the machine to cut the rod into 9 equal parts?

The book answer is 96s. Is it correct? How? I keep getting 90s.. Please advise. Thank you

Hi,

"6 equal parts" means 5 cuts
"9 equal parts" means 8 cuts

5 cuts → 60 s
1 cut → 12 s
8 cuts → 96 s


Hope this helps.

speedmaths
.

[belnanna]

Can someone please help with this question please.. Thank you very much in advance..

Peter's age is 1/7 of his grandmother's. His grandmother will be 89 years old in 5 years time. In how many years time will Peter's age be 5/9 of his grandmother's?

[tanxexy]

Can someone please help with this question please.. Thank you very much in advance..

Peter's age is 1/7 of his grandmother's. His grandmother will be 89 years old in 5 years time. In how many years time will Peter's age be 5/9 of his grandmother's?

Hi belnanna,

His grandmother is 89 - 5 = 84 years old now.
So, Peter is 1/7 of 84 = 12 years old now.

Age difference = 84 - 12 = 72 years old (constant difference)

For Peter to be 5/9 of his grandmother's age, the difference will be 4/9 = 72
----------- => 5/9 = 72/4 x 5 = 90
Therefore, Peter should be 90 years old and grandmother 162 years old for him to be 5/9 of her age.

Ans: 90 - 12 = 78 years' time

(The answer does not seem to be "realistic" but should be mathematically correct.)

cheers...

[belnanna]

Can someone please help with this question please.. Thank you very much in advance..

Peter's age is 1/7 of his grandmother's. His grandmother will be 89 years old in 5 years time. In how many years time will Peter's age be 5/9 of his grandmother's?

Hi belnanna,

His grandmother is 89 - 5 = 84 years old now.
So, Peter is 1/7 of 84 = 12 years old now.

Age difference = 84 - 12 = 72 years old (constant difference)

For Peter to be 5/9 of his grandmother's age, the difference will be 4/9 = 72
----------- => 5/9 = 72/4 x 5 = 90
Therefore, Peter should be 90 years old and grandmother 162 years old for him to be 5/9 of her age.

Ans: 90 - 12 = 78 years' time

(The answer does not seem to be "realistic" but should be mathematically correct.)

cheers...

Thank you dear.

[tanxexy]

Thank you dear.

Hi belnanna, you are welcomed

Btw, where did this question come from? It is rather "cruel" as a child might be puzzling where he had gone wrong when he got such "bizarre" ages as answers. He might start to doubt himself and try to work out a different approach towards getting a more "realistic" answer.

On the other hand, this question also challenges the students to be very sound with their mathematical understanding and have the confidence to stand by it.

cheers...

[belnanna]

Thank you dear.

Hi belnanna, you are welcomed

Btw, where did this question come from? It is rather "cruel" as a child might be puzzling where he had gone wrong when he got such "bizarre" ages as answers. He might start to doubt himself and try to work out a different approach towards getting a more "realistic" answer.

On the other hand, this question also challenges the students to be very sound with their mathematical understanding and have the confidence to stand by it.

cheers...

Hi,

Its from a future school in Bukit Panjang in the form of a practice paper..

[tanxexy]

Thank you dear.

Hi belnanna, you are welcomed

Btw, where did this question come from? It is rather "cruel" as a child might be puzzling where he had gone wrong when he got such "bizarre" ages as answers. He might start to doubt himself and try to work out a different approach towards getting a more "realistic" answer.

On the other hand, this question also challenges the students to be very sound with their mathematical understanding and have the confidence to stand by it.

cheers...

Hi,

Its from a future school in Bukit Panjang in the form of a practice paper..

I see...btw, what do you mean by "future school"? The school is not officially opened yet?

[Daddy]

Hi all,
I have 2 questions to ask.



THANK ALL..

[jojoberry]

Hi all,
I have 2 questions to ask.


THANK ALL..

triangle BPC is 1/4 of the rectangle. (because P is the midpoint of the width)
so the rectangle's area is 24 x 4 = 96

the area of triangle QPD should be 2/3 of 24 = 16

area of quad = 96 - 24 - 16 - 16 = 40

[jojoberry]

Hi all,
I have 2 questions to ask.


THANK ALL..

if you let 100% be 10 units, then

10B = 10G + 90

after 80% B and 30% girls left
--> 2B + 18 (boys left)
--> 7G (girls left)

7G = 4B + 36 ( girls are twice number of boys left)

10B = 10G + 90 -> 1B = 1G + 9 -> 4B = 4G + 36

so

7G = (4G + 36 ) + 36
3G = 72
1G = 24
1B = 24 + 9 = 33
10B + 90 = 330 + 90 = 420 (ans)