it's 100rpm...no?MathWithModels wrote:Question:

A circular wheel of diameter 35cm makes 100 revolutions in 1 minute.

Calculate the distance covered by the wheel in half an hour. Express your answer in km.

Answer:

Radius of the wheel: 35 / 2 = 17.5 cm

Circumference of the wheel: 2 x Pi x Radius = 2 x 3.14 x 17.5 cm = 109.9 cm

Distance covered by the wheel in 1 minute = 109.9 x 60 = 6594 cm

Distance covered by the wheel in half an hour = 6594 x 30 = 197820 cm = 1.9782 km

## Q&A - PSLE Math

- Nebbermind
- KiasuGrandMaster
**Posts:**16632**Joined:**Tue Dec 22,**Total Likes:**168

### Re: Q&A - PSLE Math

### Re: Q&A - PSLE Math

need help with the following questions

Q1. Arnold and Sandy were given some money each. If Arnold spent $25 and Sandy spent $75 each day, Arnold would still have $2100 while Sandy would have spent all her money. If Arnold spent $75 and Sandy spent $25 each day, Arnold would still have $900 while Sandy spent all her money. How much money was given to each of them?

Q2. At first Edwin had some $10 and $2 notes in the ratio of 3 : 8. After exchanging 2 $10 notes for $2 notes, the ratio of $10 to $2 becomes 1 : 3. How much did money did Edwin have at first?

Q3. There are 260 students in a school. 30% of them were girls while the rest were boys. When the school reopened, more student were admitted. The new students had boys and girls in the ratio of 5 : 4. After new students were admitted, 40% of the students was girls.

a. How many girls were admitted?

b. How many students were there in the end?

Q1. Arnold and Sandy were given some money each. If Arnold spent $25 and Sandy spent $75 each day, Arnold would still have $2100 while Sandy would have spent all her money. If Arnold spent $75 and Sandy spent $25 each day, Arnold would still have $900 while Sandy spent all her money. How much money was given to each of them?

Q2. At first Edwin had some $10 and $2 notes in the ratio of 3 : 8. After exchanging 2 $10 notes for $2 notes, the ratio of $10 to $2 becomes 1 : 3. How much did money did Edwin have at first?

Q3. There are 260 students in a school. 30% of them were girls while the rest were boys. When the school reopened, more student were admitted. The new students had boys and girls in the ratio of 5 : 4. After new students were admitted, 40% of the students was girls.

a. How many girls were admitted?

b. How many students were there in the end?

### Re: Q&A - PSLE Math

Scenario 1 :Spending Ratiocindy28 wrote:need help with the following questions

Q1. Arnold and Sandy were given some money each. If Arnold spent $25 and Sandy spent $75 each day, Arnold would still have $2100 while Sandy would have spent all her money. If Arnold spent $75 and Sandy spent $25 each day, Arnold would still have $900 while Sandy spent all her money. How much money was given to each of them?

A : S

25 : 75

Total Arnold had = 25u + $2100

Total Sandy had = 75u ->She spent all, which is also what she had

Scenario 2 Sepnding Ratio

A : S

75 : 25

Total Arnold had = 75p + $900

Total Sandy had = 25p

25p=75u , Base on Sally's money

75p = 225u

25u + 2100 = 225u + 900 , Base on what Arnold had

200u = 1200

u = 6

Arnold had 25u + 2100 = $2250 #####

Sally had 75u = $450 #####

### Re: Q&A - PSLE Math

2 piece of $10 notes will exchange for 10 piece of $2 notescindy28 wrote:need help with the following questions

Q2. At first Edwin had some $10 and $2 notes in the ratio of 3 : 8. After exchanging 2 $10 notes for $2 notes, the ratio of $10 to $2 becomes 1 : 3. How much did money did Edwin have at first?

Code: Select all

```
$10 : $2
3u : 8u
-2 +10
1p : 3p
```

8u + 10 = 3p

9u - 6 = 3p

8u + 10 = 9u - 6

u = 16

At 1st,

Pieces of $10 notes = 3u = 48

Pieces of $2 notes = 8u = 128

Value of $10 notes = $480

Value of $2 notes = $256

Total he had at first = $480+$256 = $736 ##

### Re: Q&A - PSLE Math

Before,cindy28 wrote: Q3. There are 260 students in a school. 30% of them were girls while the rest were boys. When the school reopened, more student were admitted. The new students had boys and girls in the ratio of 5 : 4. After new students were admitted, 40% of the students was girls.

a. How many girls were admitted?

b. How many students were there in the end?

girls = 30% of 260 = 78

Boys = 70% of 260 = 182

Code: Select all

```
Boys : Girls
182 78
+5u +4u
60p 40P
```

78 + 4u = 40p --(2)

(2) X 1.5,

117 + 6u = 60p

117 + 6u = 182 + 5u

u = 65

a) Girls admitted = 4u = 260 ###

b) from (2)

78 + 260 = 40p

40p = 338

p=8.45

In the end there are 100p student = 100 (8.45) = 845 ###

Last edited by Ender on Sat May 28, 2016 2:20 pm, edited 1 time in total.

### Re: Q&A - PSLE Math

is it possible to solve this question without using guess n check or quadratic equation?

the area of a rectangle is 84cm2. the length is 5cm more than the width. find the length of the rectangle.

thanks!

the area of a rectangle is 84cm2. the length is 5cm more than the width. find the length of the rectangle.

thanks!

- alfretztay
- KiasuGrandMaster
**Posts:**1199**Joined:**Sun Sep 12,**Total Likes:**5

### Re: Q&A - PSLE Math

Without using guess and check or quadratic equation, I would solve the above question as follows :westbb wrote:is it possible to solve this question without using guess n check or quadratic equation?

the area of a rectangle is 84cm2. the length is 5cm more than the width. find the length of the rectangle.

thanks!

84 = 1 x 84 = 2 x 42 = 3 x 28 = 4 x 21 = 6 x 14 = 7 x 12

Observe that 12 - 7 = 5 (the length is 5cm more than the width)

Thus, length = 12

Ans : 12cm.

### Re: Q&A - PSLE Math

L x B = 84westbb wrote:is it possible to solve this question without using guess n check or quadratic equation?

the area of a rectangle is 84cm2. the length is 5cm more than the width. find the length of the rectangle.

thanks!

L - B = 5

Factoring 84 with 2 factors within a difference of 5,

84 = 7 x 12 = 7 x (7+5)

**Hence length -> 12**

- questionable_i
- BrownBelt
**Posts:**535**Joined:**Sat Oct 10,**Total Likes:**1

- EconsPhDTutor
- GreenBelt
**Posts:**182**Joined:**Sat Jan 23,**Total Likes:**1

### Re: Q&A - PSLE Math

questionable_i wrote:Can anyone help me with these questions? Thank you

(13) The shaded triangle in △ABC has the same base as, but ½ the height of △ABC. Thus, it has ½ the area of △ABC.

Thus ▱ABCD has area 4 × 14 = 56 cm².

(15) Let F be the number of 5-bead packets and S be the number of 7-bead packets.

Then the total number of packets is F + S and the total number of beads is 5F + 7S. The ratio of the former to the latter is (F + S) ÷ (5F + 7S). We are told that this ratio is 5:29.

Cross-multiplying, we have 29 (F + S) = 5 (5F + 7S).

Doing the algebra, 4F = 6S. Rearranging, S:F = 4:6. That is, there are four 7-bead packets for every six 5-bead packets. Hence, 40% or ⅖ of all packets contain 7 beads.

Hope this helps and feel free to ask for any clarifications.

- Dr. Choo Yan Min

www.EconsPhDTutor.com

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