Q&A - PSLE Math

[Hifive]

tianzhu:

Hifive:

Jack, Sam and Nasim walked at a constant speed of 60 m/min, 70 m/min and 80 m/min respectively. Setting off at the same time, Jack and Sam walked from Village X to Village Y while Nasim walked from Village Y to Village X. Nasim passed Jack 10 minutes after passing Sam. Find the distance between the two villages.

Hi Hifive

There are two or three ways to go about this question.

As in any questions on “Speed”, it’s always useful to draw a diagram and put in the information bit by bit.

One neat way is to use the concept of combined speed.

Distance ------ Speed*Time

Jack and Nasim had a combined speed of 140m/min.
Jack and Sam had a combined speed of 150m/min.

Ratio of speed ------- Jack and Nasim: Jack and Sam --------14:15

As we know the faster the speed, the lesser the time taken.
So their time ratio ------- Jack and Nasim: Jack and Sam --------15:14

The difference is 1 unit
1 unit ------10 mins

Jack will meet Nasim in 150 mins
And Jack will meet Sam in 140 mins

Hence, distance between the two villages ------ (150*140) or (140*150)

The answer is 21000m or 21km.

Best wishes

Hi tianzhu

Thanks for your help!

Need to clarify :

I do not understand why Jack and Sam had a combined speed of 150m/min, I've got it as 130m/min ? Pls advise.

[tianzhu]

Hifive:

Hi tianzhu

Thanks for your help!

Need to clarify :

I do not understand why Jack and Sam had a combined speed of 150m/min, I've got it as 130m/min ? Pls advise.

Hi

I am sorry, it should be read as Sam and Nasim had a combined speed of 150m/min.

Best wishes

[Hifive]

Hi tianzhu


Got it. Thank you, thank you!

[tianzhu]

Hifive:

Hi tianzhu


Got it. Thank you, thank you!

Hi Hifive

You're welcome.

Best wishes

[2centsworthy]

:thankyou:

WCW:

2centsworthy:

Please help to solve the following:

Ron had some chocolates and sweets. If Ron sold 18 chocolates and 24 sweets each day, there would still be 25 chocolates left when all the sweets were sold. If Ron sold 13 chocolates and 30 sweets each day, he would still have 139 chocolates left when all the sweets were sold. How many chocolates and sweets did Ron have?

My method is find the common multiple for 24 and 30. think someone might have an easier and faster way?

Common muliples of 24 and 30
120, 240, 360

C : S
18 : 24
18*15 : 24*15
+25

C : S
13 : 30
13*12 : 30*12
+139

C=295
S=360

[Daddy]

Hi,


I have a question to ask.

1. grandpa had a farm. He kept 89 goats and chickens. The total number of legs the animals had was 264 legs. How many chickens did grandpa have?

If use guess and check methode would be very long time to find the anwer. Is there any short way to solve above question?
Thanks…

[MathIzzzFun]

Daddy:

Hi,


I have a question to ask.

1. grandpa had a farm. He kept 89 goats and chickens. The total number of legs the animals had was 264 legs. How many chickens did grandpa have?

If use guess and check methode would be very long time to find the anwer. Is there any short way to solve above question?
Thanks....

Hi

use the assumptive method...

assume all are goats OR all are chickens first.

say, all are goats, then total legs = 4 x 89 = 356
\"extra\" legs = 356 - 264 = 92
the \"extra\" legs are due to counting chickens as goats.. ie 2 extra legs counted, so number of chickens = 92/2 = 46
89 - 46 = 43 goats

so, 46 chickens & 43 goats.

cheers.

[dnsy]

MathIzzzFun - Thanks!

[ozora]

need quick help:

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 plates.Given that there were 120 fewer plates than cups in total,how many plates were there?
Thanks in advance

[MathIzzzFun]

ozora:

need quick help:

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 plates.Given that there were 120 fewer plates than cups in total,how many plates were there?
Thanks in advance

Hi

this is a variation of the typical \"counting coins\" problem sum.

There are 120 more cups than plates...& 12 more blue boxes (cups) than red boxes (plates)

each blue box has 30 less cups than plates in red box.

make the number of boxes the same - either add red boxes, or remove blue boxes. Since we are looking for number of plates (red boxes), we remove blue boxes.

remove 12 blue boxes so that there are now equal number of boxes.
12 x 120 cups = 1440 cups, there are now 1440 - 120 = 1320 lesser cups than plates in the boxes.

each blue box has 30 less cups than plates in red boxes, 1320 / 30 = 44
there are 44 red boxes and 44+12 = 56 blue boxes

number of plates = 44 x 150 = 6600

cheers.