Q&A - PSLE Math

[pixiedust]

Winx5015:

There were 4/5 as many sheep as horses in a zoo. After 92 horses were sent away, the percentage of horses dropped to 30%. Find the number of sheep in the zoo.

before :
sheeps -> 4U
horses -> 5U

after :
sheeps -> 7U
horses -> 3U

92 horses were sent away, no change in number of sheeps so make sheeps the same in before and after :

before :
sheeps -> 4U x 7 = 28U
houses -> 5u x 7 = 35U

after :
sheeps -> 7U x 4 = 28U
horses -> 3U x 4 = 12U

23U->92
U->4
Ans: There are 112 sheeps.

[anneshirleygilbert]

Hi. I need some help for the following questions:


1) Tom’s present age is thrice Sally’s age some years ago. Conversely, Sally’s present age is Tom’s age the same number of years ago. Given that the sum of their present ages is 30 years, how old is Tom now?

2)When Kok Hwa’s age was twice Bala’s age, Mike’s age was 30. When Mike’s age was twice Kok Hwa’s age, Bala’s age was 21. Given that Mike was the oldest among the three persons, find Bala’s age when Mike was 62 years old.

If possible, not by algebra, please.
Thank you in advance.

[tianzhu]

anneshirleygilbert:

Hi. I need some help for the following questions:

1) Tom's present age is thrice Sally's age some years ago. Conversely, Sally's present age is Tom's age the same number of years ago. Given that the sum of their present ages is 30 years, how old is Tom now?

Hi

Please follow this link.

http://www.kiasuparents.com/kiasu/forum/viewtopic.php?f=68&t=25129&start=430

http://farm8.staticflickr.com/7035/6812082325_7bb0b1b14f_z.jpg\">

Best wishes

[tianzhu]

anneshirleygilbert:

2)When Kok Hwa's age was twice Bala's age, Mike's age was 30. When Mike's age was twice Kok Hwa's age, Bala's age was 21. Given that Mike was the oldest among the three persons, find Bala's age when Mike was 62 years old.

Hi

For Q2,I'll provide some pointers instead of drawing MD.

Case 1
Bala ----- 1 unit
KH ----- 2 units
Mike ------ 30

Difference in age between KH and Bala ----- 1 unit

Difference in age between Mike and KH ----- 30 – 2 units

Case 2
Bala ----- 21
KH ----- 21 + 1 unit
Mike ------ (21 + 1 unit) + (21 + 1 unit)
Difference in age between Mike and KH ----- 21 + 1 unit

Difference in age between two people remains the same.

30 – 2 units ----- 21 + 1 unit

3 units ----- 9
1 unit ----- 3

When Mike’s age was 30, Bala was 3 years old.

62 – 30 ------ 32

Therefore , Bala ----- 3 + 32 ------ 35 years old.

Best wishes

[fightingmom]

MathIzzzFun:

fightingmom:

Hi hi,


Can someone please help with the following 2 maths questions ...

(1) Varsha had some 20-cent and 50-cent coins.
7/8 of the coins were 20-cent coins and the rest were 50-cent coins.
After Varsha had spent $72.50 worth of 50-cent coins and 5/7 of the 20-cent
coins, she had 2/7 of the coins left.
Find the total amount of money Varsha left.

Thank you in advance !

Hi

Q1..

http://i43.tinypic.com/4ind4x.jpg\">

cheers.

=========================
Hi MathIzzzFun,

Thank you so much for your help! Sorry i take so long to reply cos facing some problem with my PC earlier on!

Once again, :thankyou:

[fightingmom]

small:

HTH for question 2...cheers!!


J : K : L
640-9U : 5U : 4U -> x 2
640-18U : 10U : 8U (at first)


After James and KEith had each lost half of their toy cars,the ratio become:
320 - 9U : 5U : 8U (after)


Given Keith had 100 more toy cars than James after they lost half their toy cars.
5U - 100 = 320 - 9U
14U = 420
1U = 30

James had 640-9U at first
= 640 - 9U
= 640 - 540
= 100

James had 100 toys cars at first

Hi Hi,

Just want to thank you for helping me solve the above question! So glad that i can find so many gurus here ! :rahrah:

Once again, :thankyou:

[anneshirleygilbert]

When Mike’s age was twice Kok Hwa’s age, Bala’s age was 21. Given that Mike was the oldest among the three persons, find Bala’s age when Mike was 62 years old.


Case 2
Bala ----- 21
KH ----- 21 + 1 unit
Mike ------ (21 + 1 unit) + (21 + 1 unit)
Difference in age between Mike and KH ----- 21 + 1 unit

Hello tianzhu,

Thank you for your prompt reply.

I am hung up on KH’s age being (21 + 1unit) when Bala was 21. Can you please help?

Thank you.

[tianzhu]

anneshirleygilbert:

I am hung up on KH's age being (21 + 1unit) when Bala was 21. Can you please help?

Hi anneshirleygilbert

Good Morning.

Don’t worry too much about it now.

Please go out and enjoy your wan ton mee first.

I’ll find time to draw the MD, most probably after twelve today.

Best wishes

[small]

anneshirleygilbert:

When Mike's age was twice Kok Hwa's age, Bala's age was 21. Given that Mike was the oldest among the three persons, find Bala's age when Mike was 62 years old.


Case 2
Bala ----- 21
KH ----- 21 + 1 unit
Mike ------ (21 + 1 unit) + (21 + 1 unit)
Difference in age between Mike and KH ----- 21 + 1 unit

Hello tianzhu,

Thank you for your prompt reply.

I am hung up on KH's age being (21 + 1unit) when Bala was 21. Can you please help?

Thank you.

Hi anneshirleygilbert,

Hope this helps.

The key point is Difference in age between two people remains the same

From case 1, we knew that the different in age between Bala and Kok Hwa is 1 unit;
so for case 2, when Bala is 21, Kok Hwa is 21 + 1 unit

[tianzhu]

Hi anneshirleygilbert


“Age Questions\" are popular in primary school maths.

Before putting pen to paper, students should realise that the difference in age between two people will always remain the same.

I am hung up on KH's age being (21 + 1unit) when Bala was 21. Can you please help?

Bala's age is 1u
KH's age is 2u

Difference in age ----- 1u

This difference remains the same.

So when Bala was 21, KH was (21+1u) as shown in the MD.

Usually two scenarios are given, current and some years ago or some years later.

You may work using MD or UM.

As usual, I’ve drawn more MD than it is necessary, try to get your child to understand the logic and consolidate the steps.

Have a happy weekend.

Best wishes.

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