Q&A - PSLE Math

[Priskhipo]

heutistmeintag:

ok, I need help on this P6 problem. No simultaneous equations pls.


There are several red balls and white balls on the table.
If 1 red ball and 1 white ball are removed together each time until no red balls are left on the table, then the number of remaining white balls is 50.
if 1 red ball and 3 white balls are removed together each time until no white balls are left on the table, then the number of remaining red balls is also 50.
Find the total number of red balls and white balls at first.

Many thanks in advance!

Hi,

Solution:



http://www.postimage.org/image.php?v=aV1uIU2S

[heutistmeintag]

Thanks, Priskhipo. Could you elaborate on the 2nd part pls?

[Priskhipo]

heutistmeintag:

Thanks, Priskhipo. Could you elaborate on the 2nd part pls?

Hi heutistmeintag,

Referring to Model representing White Balls:
1 Part + 50 in 1st scenario = 3 units in 2nd scenario
because it says for every 3 white balls & 1 red ball are removed each time till no white ball left. Therefore all of the white balls are divided into 3 units.
From the 2 models, 1 Part = 2 units and 50 = 1 unit

Referring to Model representing Red Balls:
(1 unit = 50) is confirmed in 2nd scenario.
1 unit of Red Balls is removed and left with 50.
(Remember 1 Part = 2 units?)

Hope this can help you.

[suiyuan]

Thank you for your time


At a party, Sarah distributed 18 sweets to each of the boys and 20 sweets to each of the girls and had 48 sweets left. If she had distributed 20 sweets to each of the boys and 18 sweets to each of the girls instead, she would have 32 sweets left. If Sarah had 40 pupils in her class,

a) How many more boys than girls were there in her class?
b) How many sweets did she have at first?

[lizawa]

Scenario 1:


Boys : 18 sweets each
Girls : 18 sweets + 2 sweets each
Left : 48 sweets

Scenario 2 :
Boys : 18 sweets + 2 sweets each
Girls : 18 sweets each
Left : 32

So, no. of sets of 18 sweets will be the same in both scenarios.
The only difference is the sets of "2 sweets".

Difference in sets of 2 sweets = 48 - 32 = 16
16 = 8 sets of 2 sweets

(a) There are 8 more boys than girls.

(b) Total no. of pupils = 40
no. of girls = 16
no. of boys = 24
no. of sweets = (18 * 24) + (20*16) + 48 = 800

[youngmum]

How to solve these 3 questions pretty please?


(1) Mrs Tan has some pencils. If she packs them into bundles of 5 pencils in each bundles, she will have 4 extra pencils. If she packs them into bundles of 9 pencils in each bundles, she will need 7 mor epencils. How many pencils are there?

(2) At a bk fair, Tom spent $6 less than of his money on a storybook and $2 more than of his remaining money on reference books. After buying thebooks, he still had $10 left.
(a) How much money was left after he bought his story books and before hte bought the reference bk?
(b) How much money did Tom have at first?

(3) There were 2 identica flights of steps. For the first flights of steps, Siti walked up some steps adn ran 4 steps and took a total of 75 seconds. For the second flight of steps, she walked up some steps and ran 11 steps and took a total of 40 seconds. how long will siti take if she had walked up both flight of steps? Leave your answer in seconds.

TIA.

[ChiefKiasu]

youngmum:

(1) Mrs Tan has some pencils. If she packs them into bundles of 5 pencils in each bundles, she will have 4 extra pencils. If she packs them into bundles of 9 pencils in each bundles, she will need 7 mor epencils. How many pencils are there?

Standard guess and check question (Level P3)
Bundles of 5: 9, 14, 19, 24, 29, 34, 39, 44, 49, 54, 59, 64, 69, 74
Bundles of 9: 2, 11, 20, 29, 38, 47, 56, 65, 74
Answer: Total number of pencils = 74

Correction: The better answer is 29, although 74 is another possible answer.

youngmum:

(2) At a bk fair, Tom spent $6 less than of his money on a storybook and $2 more than of his remaining money on reference books. After buying thebooks, he still had $10 left.

(a) How much money was left after he bought his story books and before hte bought the reference bk?
(b) How much money did Tom have at first?

Sorry... catch no ball... less than WHAT?... more than WHAT?... the question has my logic circuits tied up in knots. Need someone to untie them for me :?

youngmum:

(3) There were 2 identica flights of steps. For the first flights of steps, Siti walked up some steps adn ran 4 steps and took a total of 75 seconds. For the second flight of steps, she walked up some steps and ran 11 steps and took a total of 40 seconds. how long will siti take if she had walked up both flight of steps? Leave your answer in seconds.

Assuming Siti walked and ran at the same constant speeds:
Time difference in running up (11-4) 7 steps = 75-40 = 35s
So additional time taken to walk up 1 step = 35/7 = 5s
Additional time taken to walk up 4 steps = 4x5 = 20s
Total time taken to walk up 2 flights of steps
= 2 x (20+75) = 190
or = 2 x (11x5 + 40) = 190

[youngmum]

Wow, chief KS, thanks. Gosh i feel so stupid.

[ChiefKiasu]

youngmum:

Wow, chief KS, thanks. Gosh i feel so stupid.

No no... we should not feel stupid... as kids, we ourselves were never exposed to such \"brain twisters\", and we taught to solve problems in the most efficient way possible. We were taught processes of solving instead of principles of understanding. That's why we find it so hard to adapt to the \"new\" math.

[ChiefKiasu]

ChiefKiasu:

youngmum:

(1) Mrs Tan has some pencils. If she packs them into bundles of 5 pencils in each bundles, she will have 4 extra pencils. If she packs them into bundles of 9 pencils in each bundles, she will need 7 mor epencils. How many pencils are there?

Standard guess and check question (Level P3)
Bundles of 5: 9, 14, 19, 24, 29, 34, 39, 44, 49, 54, 59, 64, 69, 74
Bundles of 9: 2, 11, 20, 29, 38, 47, 56, 65, 74
Answer: Total number of pencils = 74
...

Er... on closer examination, I think I overshot the smallest number that matches, which is 29 :oops: Guess I won't pass PSLE this year