Q&A - PSLE Math

[tianzhu]

Hi kancheongmum


Thank you for sharing.

Best wishes

[tianzhu]

Hi


You may wish to try these two questions.

1) Tommy had six more 50-cent coins than 20-cent coins. After he used eight 50-cent coins, the value of the 50-cent coins is $7.40 more than the value of 20-cent coins. How many coins did he have at first?

2) Some plates and cups were packed into blue and red boxes. There were 12 more blue boxes than red boxes. Each blue box contained 120 plates and each red box contained 150 cups. Given that there were 120 fewer plates than cups in total, how many plates were there?

Best wishes

[kancheongmum]

Hi all just got ACS prelim 2010 from a friend. Surprisingly in my opinion is not as challenging as the others. Came across 2 questions from the paper and like you all to try.


1)Mdm Zhang packed some beads into 14 small boxes and 15 big boxes. There were equal number of beads in each small box and equal number of beads in each big box. Each big box contained 5 more beads than each small box. 3/8 of the beads were packed in small boxes. How many beads were there in each small box? (ans 9)

2) A tank measuring 80 cm by 60 cm by 55 cm was 1/5 filled with water. A tap was turned on to fill it up with water at a rate of 9L per min. Every 30 seconds after the tap was turned on, an iron ball with a volume 500 cm3 was dropped into the tank. How many iron balls would there be in the tank when the water level reached the brim? (ans 42 iron balls)

[Vanilla Cake]

kancheongmum:

Hi all just got ACS prelim 2010 from a friend. Suprisingly in my opinion is not as challenging as the others. Came across 2 questions from the paper and like you all to try.

Hi kancheongmum,
There are the workings done by DD2 (P5) and pls help to check her workings as she is taking PSLE Maths next year (2011).Thks.

kancheongmum:

1)Mdm Zhang packed some beads into 14 small boxes and 15 big boxes. There were equal number of beads in each small box and equal number of beads in each big box. Each big box contained 5 more beads than each small box. 3/8 of the beads were packed in small boxes. How many beads were there in each small box? (ans 9)

Small: u
Big: u+5

14 Small:15 Big -> 3:5
14x5u=3(u+5)x15
70u=45u+225
25u=225
u=9

9 beads in each small box.

kancheongmum:

2) A tank measuring 80 cm by 60 cm by 55 cm was 1/5 filled with water. A tap was turned on to fill it up with water at a rate of 9L per min. Every 30 seconds after the tap was turned on, an iron ball with a volume 500 cm3 was dropped into the tank. How many iron balls would there be in the tank when the water level reached the brim? (ans 42 iron balls)

Remainder to be filled = (80x60x55)x4/5=211200 cm³
0.5 min-> 4500 cm³+500 cm³ = 5000 cm³ (1 iron ball)
211200÷5000 = 42.24 sets of 0.5 min -> 21.12 min
21.12÷0.5=42.24
Number of iron balls in the tank when the water level reached the brim= 42

VC's mum

[Chrislee]

Have the solution for Nanyang primary 2010 prelim been given? I searched through but din see it.


I need the solution for qn 16 on the pizza question & qn 17 on the white & blue marbles question.

Many thanks.

[ABCDE]

Chrislee:

Have the solution for Nanyang primary 2010 prelim been given? I searched through but din see it.


I need the solution for qn 16 on the pizza question & qn 17 on the white & blue marbles question.

Many thanks.

Hi Chrislee,
Can u post those qts? Can u also post Qt 11 on volume?
Heard tht qts are tricky.Saw in maths guru also...some poeple asking 4 it.
Can VC's mum /Uncle Tianzhu/Uncle Dharma give me the link?
Thank u in advance

[Vanilla Cake]

Chrislee:

I need the solution for qn 16 on the pizza question & qn 17 on the white & blue marbles question.

Solution for Q16 by Tianzhu @ KSP forum
Each boy -------2/9 pizza -------- 4/18pizza ------ 4 units\t\t\t\t
Each girl ------- 1/6 pizza ------- 3/18 pizza ------- 3 units\t\t\t\t
\t\t\t\t
1) Draw 3 blocks to show girls’ pizzas\t\t\t\t
2) Draw 1 block to show boys’ pizzas\t\t\t\t
3) Cut out block in (2) into 4 units, no remainder\t\t\t\t
4) Cut out 3 units in (1), leaving a remainder of 4.5 pizza\t\t\t\t
\t\t\t\t
5) 12 units ------ 3 units+4.5\t\t\t\t
9 units ---- 4.5\t\t\t\t
1 unit -----0.5\t\t\t\t
\t\t\t\t
Number of pizzas ------ (7*0.5) + 4.5 ------ 8

and

http://psle2010a.blogspot.com/2010/09/nanyang-p6-prelim-2010-p2-q16.html

and

I think this solution was given by Dharma @ KSP forum?

First let's look at the ratio of pizza eaten for each boy and girl\t\t\t\t
\t\t\t\t
Ratio of eaten for each\t\t\t\t
B : G\t\t\t\t
2/9 : 1/6\t\t\t\t
4 : 3\t\t\t\t
\t\t\t\t
But we know the girls received three x times\t\t\t\t
Ratio of Pizza received\t\t\t\t
4 : 12 (Total 16units)\t\t\t\t
\t\t\t\t
Difference 12units -> 3units = 9units\t\t\t\t
\t\t\t\t
9units --> 4.5 pizzas\t\t\t\t
16units --> ???\t\t\t\t
\t\t\t\t
9units --> 4.5 pizzas\t\t\t\t
18units--> 9 pizzas\t\t\t\t
1unit --> 1/2 pizza\t\t\t\t
16units --> 8 pizzas\t\t\t\t

Solution by Chris Rogers and Reynold Tan for Q17@ OnSponge forum
http://www.onsponge.com/forum/35-thinkingmathonsponge/4962-ratio-p6-2010-sa2-nanyang-p2-q17-pls-help.html#4983

and

http://psle2010a.blogspot.com/2010/09/nanyang-p6-prelim-2010-p2-q17.html

VC's mum

[ABCDE]

Hi VC mum,


Can u post Qt :11 from NY 2010 prelim for me.
Thanks

[ABCDE]

tianzhu:

Hi


You may wish to try these two questions.

1) Tommy had six more 50-cent coins than 20-cent coins. After he used eight 50-cent coins, the value of the 50-cent coins is $7.40 more than the value of 20-cent coins. How many coins did he have at first?

2) Some plates and cups were packed into blue and red boxes. There were 12 more blue boxes than red boxes. Each blue box contained 120 plates and each red box contained 150 cups. Given that there were 120 fewer plates than cups in total, how many plates were there?

Best wishes

Hi Tianzhu,
Please confirm wht the answers are as follows:

2) 7680 plates
1) 62 coins

[kancheongmum]

Hi VC’s mum


Your DD2 will sure ace PSLE. My DS can’t solve Q1 and he is taking PSLE in 2 weeks. He always think too much for a simple question. On the 2nd attempt he uses fraction to solve which is also the solution provided by the school, the setter of question. Just for info:

sb - small box
bb - big box

14sb —3/8
1 sb — 3/112

15 bb — 5/8 —70/112
1bb — 14/336

1sb — 3/112 — 9/336

14/336 - 9/336 — 5/336 —5 beads
1/336 — 1 bead
1 small box — 9 x 1 = 9 beads

It is ok for me as long as the working is logical and he gets the answer. Cannot do much now as PSLE is just 2 wks away, putting too much things in his head will get him confuse. I wish he can solve this way:

3u — 14 small box
5u — 15 big box
1u — 3 big box
3u — 9 big box
1 big box = 1 small box + 5 beads
9 big box = 14 small box
9 small box + 45 beads = 14 small box
5 small box ---- 45 beads
1 small box = 45/5 = 9 beads