Q&A - PSLE Math

[COOKIE64]

Please help

Kathy had 7 bags of rice at first. Then she bought a bag of rice with the mass of 24.9 kg and another bag of rice with mass of 17.6 kg . As a result , the average mass of the bags of rice increased by 2.5 kg what was the total mass of the 9 bags of rice?

[NerdyMath]

Mr Tan is (8k+10) years old now. How has two children , Rosalynn and David . Mr Tan is twice as old as Rosalynn now. David is 2k years younger than Rosalynn. How old will Mr Tan be when David turns 18 years old?

MR TAN -> 8K+10
ROSALYNN -> 4K+5
DAVID -> 2K+5

This is a constant different question.

Difference in age ->8K+10-2K+5 = 8K-2K + 10-5
= 6K+5

As the difference will always be 6k+5, we can say that if David is 1 year old, Mr tan will be 6K+5 years older than him, if David is 2 years old, Mr tan will still be 6K+5 years older than him, so when David is 18 years old, Mr tan will still be 6K+5 older than him.

18+6K+5= 6k+23 years old

[PlayfulFairy]

Please help! Thanks!
At a sale, Mr Lim bought 10 mugs of the same kind. His sister bought 8 such mugs. She also bought 3 towels at $2.50 each. Altogether, she spent $2.30 less than Mr Lim. What was the total amount of money Mr Lim and his sister spent?

[Ender]

Hi , the answer is 6K+ 23 years old Mr tan will be

After seeing Nerdymath's solution. I understood the the answer.

[COOKIE64]

Ok Thanks to all for helping me

[Ender]

Please help with these Q

Mrs Tan is 40 years old and her son is twice her daughters' sage. Mrs Lim will be thrice her Sons's age when her daughter is 12 years old .how old will Mrs Lim be when her 2 children's combined age equals to her age ?

Now,
Lim = 40 yrs
Son =2d
Daugther =d


When the daughter is 12 years old, number of years passed is (12-d) years
Daughter = 12
Son = 12 + d , Constant difference
Lim = 36 + 3d(Triple of Son) or 40 + (12 -d)

3d + 36 =52 - d
4d = 16
d = 4
Son = 8 , 2 times of daughter.

Let the number of years pass to be 'u'
(Daughter + u) + (Son +u) = (Mrs Lim + u )
(4+u) +(8+u) = (40+ u)
12 + 2u = 40 + u
u = 28

In 28 years time

Edit note: The answer is 68 years old, from 40 +28

[NerdyMath]

Please help

Kathy had 7 bags of rice at first. Then she bought a bag of rice with the mass of 24.9 kg and another bag of rice with mass of 17.6 kg . As a result , the average mass of the bags of rice increased by 2.5 kg what was the total mass of the 9 bags of rice?

9* 2.5kg=22.5kg
24.9kg+17.6kg=42.5kg
42.5kg-22.5kg=20kg
20kg/2=10kg
10kgx7=70kg
70kg+42.5kg=112.5kg

Solved by DS.

[NerdyMath]

Ok Thanks to all for helping me

You're welcome! DS is very happy to help!

[SAHMom]

Please help! Thanks!
At a sale, Mr Lim bought 10 mugs of the same kind. His sister bought 8 such mugs. She also bought 3 towels at $2.50 each. Altogether, she spent $2.30 less than Mr Lim. What was the total amount of money Mr Lim and his sister spent?

Don't forget the power of models this Fri. Good luck to all!

[mceducation1]

Help

Hi there,

Let's start with the following:

Information Given:

Dave gave 50% of the no. of his 50-cents' coins to Wayne
Wayne gave 50% of the no. of his $1 coins to Dave

After buying a buy with some $1 coins, the ratio of the no. of coins Dave had was:

No. of 50-cents coins : No. of $1 coins

1 : 2


After buying a books with some 50-cents, the ratio of the no. of coins Wayne had was:



No. of 50-cents coins : No. of $1 coins

1 : 5


Let's call the no. of 50-cents coins Dave has in the end "1 unit"

thus the no. of 50-cents coins Dave had in the end:

1 unit = 10 + 1 part
(10 represents the 10 coins Wayne had used to buy the book
$5 = 10 50-cents coins
and 1 part represents the no. of 50-cents coins Wayne had left)


No. of $1 coins:

Since the ratio of the no. of 50-cents coins Wayne had to that of the no. of $1 coins he had in the end was 1 : 5

Thus the no. of $1 coins Wayne had in the end was:

5 parts = 2 units + 16

(2 units --- becos the ratio of Dave's 50 cents coins to $1 coins was 1 : 2
and Dave had used $16 to buy a bag - which is 16 coins)


since 1 unit = 10 + 1 part
therefore 2 units = 20 + 2 parts

Thus 5 parts = 2 units + 16
is the same as 5 parts = (20 + 2 parts) + 16

5 parts = 36 + 2 parts
5 parts - 2 parts = 36
3 parts = 36
1 part = 36 divided by 3 = 12

Since Wayne had used 10 coins to buy a book,
10 + 12 = 22
Since Dave had given half of his 50 cents coins away,

Therefore there were 2 x 22 = 44 fifty cents coins
44 x 50cents = $22

Therefore the original amount that Dave had was $ 22.


Hope this helps!

SMILE!!

Michelle Choo
Mathematics Educator for 27 years