Q&A - PSLE Math

[Zhu99]

zanen:

Zhu99:

[quote=\"zanen\"]Hi thanks for the previous ans. can help me with these two. thx in advance A rabbit and a tortoise competed in a 5.2 km race. The rabbit ran at a speed of 20 km/h while the tortoise’s speed was 3 km/h. The tortoise ran continuously to complete the race. However the rabbit ran for 1 min and rested for 20 min. It ran the next 2 min and rested or 20 min. It then ran for the next 3 min and rested for 20 min and so forth. At this rate, how many minutes more would it take the rabbit than the tortoise to complete the race?

T : 5.2/3 x 60 = 104 min

R : 5.2/20 x 60 = 15.6 min --- run time

1 + 2 + 3 + 4 + 5 + 0.6 ---> 5 rest time
5 x 20 = 100

100 + 15.6 = 115.6 min --- total time of R

115.6 - 104 = 11.6

The rabbit took 11.6 min more than the tortoise to complete the race.

May I know why 5 rest time and not more? :scratchhead:[/quote]The rabbit ran for 15.6 mins.
1 + 2 + 3 + 4 + 5 + 0.6 = 15.6 --- The '+\" basically represents the rest time (period). As there are 5 '+\"s, there are 5 rest time (periods). To have the 6th rest time, the balance time should be 6 min. But the rabbit completed the race with balance 0.6 min.

[Zhu99]

zanen:

Mrs Reuten bought some pizzas for a group of children. The girls received thrice as many pizzas as the boys. There were an equal number of girls and boys. Each boy ate 2/9 of a pizza and the boys finished all the pizzas given to them. Each girl ate 1/6 of a pizza and the girls had 4½ pizzas left. How many pizzas did Mrs Reuten buy?

Pizzas received --- G : B = 3 : 1
= 3 x 4 : 1 x 4
= 12 : 4 --- To get 4 for B since boys finished all the pizzas given

Pizzas eaten --- B : G = 2/9 : 1/6 --- Equal number of girls and boys
= 2/9 x 9 : 1/6 x 9
= 2 : 3/2
= 2 x 2 : 3/2 x 2
= 4 : 3

12 - 3 = 9 u ---> 4 1/2

12 + 4 = 16 u --> 16/9 x 4 1/2 = 8

Mrs Reuten bought 8 pizzas.

[ms_lim]

Can help to explain how to solve this question?


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[Winx5015]

Hi, anyone can help me with the following questions.


(1). A train left Station X with some commuters. At the first stop, no commuters alighted and the number of commuters who boarded the train was 1/5 of the original number of commuters in the train. At the second stop, 1/4 of the commuters alighted and 58 commuters boarded the train. At the third stop, 3/7 of the commuters boarded the train. At the last stop, all 315 commuters alighted. How many commuters were there when the train left Station X?

(2). Mother baked some square, round and oval cookies. For every 3 square cookies that were baked, 2 round cookies were baked. For every 4 square cookies that were baked, 3 oval cookies were baked.
(a). Find the ratio of the number of square cookies to round cookies to oval cookies baked.
(b). After mother baked another 120 round cookies, 30% of the cookies now were round cookies. How many square cookies did the bakery bake?

(3). Hadi had 295 more sweets than Ravi. After Hadi had given away 2/5 of the sweets he had and Ravi gave away 2/3 of the sweets he had, Hadi had 329 more sweets than Ravi. How many sweets did they have altogether at first?

Thank you

[Winx5015]

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Can anyone tell me how to solve this question. Thanks

[tianzhu]

Winx5015:

(2). Mother baked some square, round and oval cookies. For every 3 square cookies that were baked, 2 round cookies were baked. For every 4 square cookies that were baked, 3 oval cookies were baked.
(a). Find the ratio of the number of square cookies to round cookies to oval cookies baked.
(b). After mother baked another 120 round cookies, 30% of the cookies now were round cookies. How many square cookies did the bakery bake?

Hi

A similar question has been discussed before.

Aunt May baked some square, round and oval cookies. For every 3 square cookies that were baked, 2 round cookies were baked. For every 4 square cookies that were baked, 3 oval cookes were baked.
(a) Find the ratio of the number of square cookies to round cookies to oval cookies baked.
(b) After Aunt May baked another 120 round cookies, 30% of the cookies now were round cookies. How many square cookies did Aunt May Bake?

Square:Round ------ 3:2 -------- 12:8

Square:Oval ------- 4:3 ------- 12:9

The units for “Square cookies” are repeated in both set of ratios, so make them the same.

Ratio of the number of square cookies to round cookies to oval cookies baked ------- 12:8:9

Squre cookies ------- 12 units

Round cookies ------- 8 units + 120

Oval cookies ------- 9 units

8 units + 120 ------- 30%

21 units ------- 70%

3 units ------- 10%

Hence, 8 units + 120 ------- 9 units

This gives 1 unit ------- 120

Number of square cookies --------12*120 ------1440

Best wishes

[Shimmer]

Need help !


1 . Mr Wang bought 4 times as many chairs as tables. He spent $2527 altogether. A table cost $13 more than a chair. The total cost of the chairs was $1121 more than the total cost of the tables.
A) how much dud he spend on tables ?
B) find the cost of each table

[KPLEE]

Shimmer:

Need help !


1 . Mr Wang bought 4 times as many chairs as tables. He spent $2527 altogether. A table cost $13 more than a chair. The total cost of the chairs was $1121 more than the total cost of the tables.
A) how much dud he spend on tables ?
B) find the cost of each table

Use \"stacking\" method
A) (2527-1121)/2= 703
B) chairs=2527-703=1823
1824/4units= 456 cost of 1 stack of chairs
703-456=247 difference bet 1 stack of T v. C
247/13=19tables
703/19=37 each

[susutoo]

please help:-)

There were 315 more adults than children at an exhibition at first. After 1/7 of the adults and 60% of the children left the exhibition, there were 462 more adults than children at the exhibition. How many people were at the exhibition at first.

[Recia Lim]

tianzhu:

Recia Lim:

Please help to solve this speed question. Thanks!

Question: Mrs Tan took 40 min to walk from her home to the market. On her return journey, she took an additional 8 min. her speed on the way back was 1km/h slower. What was the distance between her home and the market?

Hi

There are a few ways to do this question.

For this question, students may get their answers quickly using GC.

Another possibility is to use inverse proportion if students are familiar with it.

Given the same distance, speed is inversely proportional to time.

Higher speed needs less time.

Lower speed leads to more time.

Time ratio

40:48 ------- 5:6

Speed ratio ------- 6:5

1 unit ------ 1 km/h

5 units ------ 5 km/h

Distance between her home and the market ------- 5*48/60 ------- 4 km

Alternatively you may use the faster speed of 6 km/h

In this case, 6*40/60 ------ 4 km.

Best wishes

Thanks! How do we know when should we use this inverse proportion method?