Q&A - PSLE Math

[Tang]

tweet:

Tang:

[quote=\"tweet\"]Hi,


can pls help solve with this question with model diagram.TIA

There were 4 times as many apples as oranges in a box.If 60 additional apples and 9 more oranges were put into the box, the new number of apples will becomes 6 times the the new number of oranges in the box. How many apples were there in the box at first?

Thanks

Before (model)
Apples -- 4 units
Oranges -- 1 unit

After (model)
Apples -- 6 Big units
Oranges -- 1 Big unit

Redraw
Oranges -- 1 unit + 9 [Divide the Big unit]
Apples -- 4 [1 unit + 9] + 2 [1 unit + 9]

2 units + 6 x 9 --> 60
2 units --> 60 - 54 = 6
1 unit --> 6 / 2 = 3

Apples: 4 units --> 4 x 3 = 12 at first.

Hi Tang

The answer is 60 apples at first.

Thanks[/quote]Checks
4 units -- 12, 1 unit -- 3

12 + 60 = 72
3 + 9 = 12

72 / 12 = 6 times (correct)

So answer 12 apples at first is correct. [60 is added, not the original number.]

[tweet]

Hi Tang


Thanks a lot. Now i see the picture after you summarise.

[small]

Once again thanks for your time.


Question:

For every question Lilian answered correctly in a quiz, she scored 5 points. 2 points were deducted for each incorrect answer. For every 20 questions Lilian answered, 5 were wrong. She scored a total of 340 points in the quiz.

a) How many questions did Lilian answer altogether?
b) How many points less did she score because of the incorrect answer?

[tianzhu]

Hi

Hope this helps.

Other than Guess and Check, the other method which is more effective is to use Grouping.

For every 20 questions, 5 were wrong, meaning there were 15 correct ones.

Marks achieved are (15*5) – (5*2) --- 65
5 groups of 20 questions gave you (5*65) --- 325
(340-325) --- 15 marks for 3 correct answers.

a)Lilian answered (5*20) + 3 -----103 questions

b)Two ways to get the answer

Method 1
(103*5) – 340 --- 175 points

Method 2
For every wrong answer, she lost (5+2) points
Therefore, she scored (25*7) ---- 175 points less

[small]

tianzhu:

Hi

Hope this helps.

Other than Guess and Check, the other method which is more effective is to use Grouping.

For every 20 questions, 5 were wrong, meaning there were 15 correct ones.

Marks achieved are (15*5) – (5*2) --- 65
5 groups of 20 questions gave you (5*65) --- 325
(340-325) --- 15 marks for 3 correct answers.

a)Lilian answered (5*20) + 3 -----103 questions

b)Two ways to get the answer

Method 1
(103*5) – 340 --- 175 points

Method 2
For every wrong answer, she lost (5+2) points
Therefore, she scored (25*7) ---- 175 points less

Hi tianzhu,

Thanks..I think your answer are correct, I also got the same answer by using methos 1..

Angry that the given answer in the book are: a) 80; b) 140... :x :x

[Denise]

A seamstress used up 64m of lace in 10 days. Everyday the length of lace used is increased by two times, compared to the before. How many days did she take to use a length of 1/4m

[mrswongtuition]

Denise, is there a typo error? She uses 64m a day, how long she takes to use 1/4m? Isn’t 1/4m = 25cm?

[corneyAmber]

mrswongtuition:

Denise, is there a typo error? She uses 64m a day, how long she takes to use 1/4m? Isn't 1/4m = 25cm?

No mistake and she uses 64m in 10 days not a day. Hence answer is 2 days.

http://i724.photobucket.com/albums/ww246/ks2me/P6Mathlace-1.jpg\">

[mrswongtuition]

Oh! haha! That’s the problem when you try to do maths questions while cooking and watching tv!

[tianzhu]

Denise:

A seamstress used up 64m of lace in 10 days. Everyday the length of lace used is increased by two times, compared to the before. How many days did she take to use a length of 1/4m

Hi, you may wish to check on this sentence again.

Everyday the length of lace used is increased by two times, compared to the before.

Is it more appropriate to replace by with to?

Everyday the length of lace used is increased to two times, compared to the before.