Q&A - PSLE Math

[tianzhu]

htn:

my friend's ds answer is 22pair and his classmates answer is different from him, teacher marked both correct. we are very confuse which is the correct answer?

Hi

Based on your reply, am I right to say that two different answers are marked correct by the teacher? One is 22. what is the other?

A pair of hamsters can produce a pair of baby hamsters every month. The baby hamsters take a month before they can reproduce another pair of baby hamsters.How many pairs of hamsters (adult and baby) will there be by the end of 6 months?

In answering this question, one has to make assumptions.

Please refer to articles on Fibonacci Sequence, the assumptions made on rabbits are:
[list]

[Hifive]

Hi all


Need help with this question:

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.

Thanks in advance.

[raghupavithra]

the total surface area of a cube is364cm2. find the volume of the cube.

pls help this question

[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.
Sam and Nasim 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

[tianzhu]

raghupavithra:

the total surface area of a cube is364cm2. find the volume of the cube.

pls help this question

Hi

I assume that students are allowed to use the calculators for your question.

A cube has 6 surfaces.
Area of 1 surface ------ 364/6 ------ 60.67cm2

A cube has equal sides.
Length or breadth of 1 side ------- 7.79 (square root of 60.67, use the calculator)

Volume of cube ------- L*B*H -------- 7.79*7.79*7.79 --------472.73cm3

Best wishes

[dnsy]

Hi. Need help with this question:


At first, 25% of Kumar’s money was the same as 33-1/3% of Lily’s money. Lily’s father gave her $80 later, while Kumar spent $325. In the end, Lily has 2-1/2 times as much money as Kumar.
(a) How much money did Kumar have at first?
(b) How much money did Lily have in the end?

Thanks!

[MathIzzzFun]

dnsy:

Hi. Need help with this question:


At first, 25% of Kumar's money was the same as 33-1/3% of Lily's money. Lily's father gave her $80 later, while Kumar spent $325. In the end, Lily has 2-1/2 times as much money as Kumar.
(a) How much money did Kumar have at first?
(b) How much money did Lily have in the end?

Thanks!

Hi

Kumar : Lily = 1/4 : 1/3 = 4u : 3u

so 4u -325 : 3u + 80
= 2 : 5

cross-multiply :
20u - 1625 = 6u + 160
14u = 1785
u = 127.5

a) 4u = 4 x $127.50 = $510
Kumar had $510 at first.

b) 3u + 80 = 3 x $127.5 + 80 = $462.50
Lily had $462.50 in the end.

cheers.

[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!