Q&A - PSLE Math

[Nebbermind]

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

it's 100rpm...no?

[cindy28]

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?

[Ender]

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?

Scenario 1 :Spending Ratio
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 #####

[Ender]

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?

2 piece of $10 notes will exchange for 10 piece of $2 notes

Code: Select all

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

3u - 2 = 1p
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 ##

[Ender]

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?

Before,
girls = 30% of 260 = 78
Boys = 70% of 260 = 182

Code: Select all

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

182 + 5u = 60p --(1)
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 ###

[westbb]

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!

[alfretztay]

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!

Without using guess and check or quadratic equation, I would solve the above question as follows :

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.

[sushi88]

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 x B = 84
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]

Can anyone help me with these questions? Thank you

[EconsPhDTutor]

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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