Q&A - PSLE Math

[ooptimizer]

Thank you!

[tianzhu]

Hi MathIzzzFun


Good Morning.

Currently, I believe you are the only tutor offering solutions in this thread.

As a daddy, I would like to take this opportunity on Teachers’ Day to offer my heartfelt appreciation to you.

Best wishes

[TT2]

Hi… Need help on this qn. Thanks in advance.


In a shooting practice, Ben obtained the scores of 5, 7, 8 and 9 after shooting four times. The highest possible whole number score that Ben might score for each shot is not more than 10. After another three shots, ben’s average score became 8. Then he fired another three shots and his average score became 8.5. He scored a total of five 9s in all the ten shots. Find Ben’s score for each of the last three shots.

[MathIzzzFun]

tianzhu:

Hi MathIzzzFun


Good Morning.

Currently, I believe you are the only tutor offering solutions in this thread.

As a daddy, I would like to take this opportunity on Teachers’ Day to offer my heartfelt appreciation to you.

Best wishes

Thank you, tianzhu.

Have a great break!

cheers.

[MathIzzzFun]

TT2:

Hi... Need help on this qn. Thanks in advance.


In a shooting practice, Ben obtained the scores of 5, 7, 8 and 9 after shooting four times. The highest possible whole number score that Ben might score for each shot is not more than 10. After another three shots, ben's average score became 8. Then he fired another three shots and his average score became 8.5. He scored a total of five 9s in all the ten shots. Find Ben's score for each of the last three shots.

Hi

Total score for 1st 4 shots = 5 + 7 + 8 + 9 = 29
Total score for 7 shots = 7 x 8 = 56, so total score for 5th-7th shot = 56-29 = 27
Total score for 10 shots = 10 x 8.5 = 85, total score for 8th - 10th shot = 85 - 56 = 29 ---> 10,10,9 since there are a total of five 9s , so the 5th -7th are all 9s

Therefore, scores for the last three shots : 10,10,9 (in any order)

[TT2]

Thank you, MathIzzzfun! U r a genius

[tianzhu]

ooptimizer:

Thank you!

Hi

You're welcome.

Best wishes

[dnsy]

Appreciate anyone’s help on this question:


Mr lee left town M and travelled towards town N at an average speed of 80km/h. An hour later, mr Ong left town M and travelled towards town N at an average speed of 100km/h. Mr Ong passed town Q which was halfway between town M and town N 30 minutes earlier than mr Lee. If mr Ong reached town N at 10 pm , at what time did mr Lee leave town M for town N ?

Thanks!

[tianzhu]

dnsy:

Mr lee left town M and travelled towards town N at an average speed of 80km/h. An hour later, mr Ong left town M and travelled towards town N at an average speed of 100km/h. Mr Ong passed town Q which was halfway between town M and town N 30 minutes earlier than mr Lee. If mr Ong reached town N at 10 pm , at what time did mr Lee leave town M for town N ?

Hi

There are a few ways to go about this question.

For question on “Speed”, it helps to draw a simple diagram to show the relationships between two motorists on a timeline.

Using,the formula, Distance ------ Speed*Time with logical reasoning,

Head start by Mr Lee ------- 80km (1*80)

Time taken by Mr Ong to catch up with Mr Lee ------- 80/(100-80) ------- 4h

30mins -----1/2h
½ *80 -------40
40/20 ------ 2h (Mr Ong took another 2h to be 20km ahead of Mr Lee @midpoint.)

Mr Ong took a total of 6h to reach the midpoint.

Time taken by Mr Ong for the whole journey ------2*6 ------12h

Working backwards from 10pm,Mr Ong started his journey@10am

Hence, Mr Lee started @9am.

For students who are familiar with inverse proportion, here's an alternative.

From Town M ------ Town Q, Mr Ong took (1+0.5) or 1.5h less than Mr Lee.(half)
From Town M -------Town N, Mr Ong took (2*1.5) or 3h less than Mr Lee.(whole)

Speed Ratio
MrOng:Mr Lee ------ 100 :80 ------5:4

Time Ratio
MrOng:Mr Lee ------ 4:5

1 unit ----- 3h
Mr Ong ------4 units ------12h

Working backwards from 10pm,Mr Ong started his journey@10am

Hence, Mr Lee started @9am.

Best wishes

[Chan09]

Appreciate some help

A had a total of 2050 black and red marbles. He lost 3/5 of his black marbles and bought 150 red marbles. As a result the no. of red marbles he had was 1/4 of the remaining black. How many more black than red marbles he had at first?
Ans: 1950