Tutor MathsGuru: Ask me for your burning Maths questions!

[mathsguru]

ttyh:

I'm sorry, I didn't meant to be funny. But my 8yrs old ds answered (1) but got it wrong...

Pls....teach me!!

The difference between 516 and ? is 381.
What is the missing number in the box above?
(1) 135
(2) 137
(3) 877
(4) 897

Hi TTYH,

Answers can be both 516 - 381 = 135 (1) and 516 + 381 = 897 (4). You should clarify with your child's teacher.

Regards,
MathsGuru

[mathsguru]

firebird:

Dear mathsguru


Good morning.

Please help me on the following question:

1) There were 850 marbles in box A and 70 marbles in Box B. When an equal number of marbles were added into each box, the ratio of the number of marbles in A to that in B is 5:1.
How many marbles were added into both boxes?

I tried this quesion for an hour or so, I give up.

Many thanks
firebird

Hi Firebird,

Here's my solution.


MathsGuru

http://www.postimage.org/image.php?v=PqzE1Ii

[mathsguru]

KSP:

Hi mathsguru, I have the working for these 2 questions from Dharma but can you show me the model method to solve them? Thanks.


1. Container A contains 250 red marbles and 200 blue marbles. Container B contains 600 red marbles and 150 blue marbles. How many red and blue marbles must be moved from Container A to Container B such that 25% of the marbles in Container A are red and 75% of the marbles in Container B are red? Ans: 350


2. In a math competition, participants can obtain 4 possible award: Gold, Silver, Bronze and Participation. 3/7 of the participants obtained Gold awards, 1/4 of the them obtained Silver awards, and 1/6 of them obtained Bronze awards. Given that there were less than 100 participants taking the competition,
a) How many participants obtained the awards for Participation? Ans: 13
b) How many more participants obtained Gold awards then Bronze awards? Ans: 22

Hi KSP,

Actually I've solved Question 1 before, but I guess you must have missed it. Here's the solution:

http://www.postimage.org/image.php?v=aVl7LP0

As for question 2, I'm afraid my recommended solution is not to draw models but rather, use fractions to solve. This is a good example of a question that will take a long time to draw the model since the common denominator is very big. Nevertheless, if you wanna see a simple visual representation, I've it here:

http://www.postimage.org/image.php?v=aVlcQ5i

Cheers,
MathsGuru

[CoffeeCat]

freakmum:

Mathsguru, how to solve this question?

If alan gives ben 6 sweets, the ratio of the number of sweets Alan will have to the number of sweets Ben will have is 2:5.
If Ben gives alan 8 sweets, the ratio of the number of sweets alan will have to the number of sweets ben will have is 1:2.
How many sweets did alan have at first?

There are many ways to solve such a question, notably using models or algebra. However I will use the ratio method.

In ratio questions, its best to find a \"common denominator\" or sth that stays constant in both ratios. In other questions its the difference, in this its the total number of sweets.

Ratio of the no. of sweets
after the first transfer Alan : Ben : Total
2 : 5 : 7
= 6 : 15 : 21

after the second transfer 1 : 2 : 3
= 7 : 14 : 21

Notice that the no. of sweet Alan had in reality is somewhere between the 6 units worth and 7 units worth. When he gave away 6 he will have 6 units worth and when he received 8 he will have 7 units worth. Therefore 1 unit worth of sweets = 6+ 8 = 14.
no. of sweets alan had at first = (6*14) + 6 = 90

[mathsguru]

KSP:

I need help on the 2 questions below.


1. The figure below is not drawn to scale. Given that the area of WXYZ is 40cm sq, find the area of the shaded part. Ans: 68cm sq

http://www.postimage.org/image.php?v=aVjVKHJ

2. The figure below is made up of two identical right-angled triangles, a small square and a big square. The parimeter of the shaded region is 50cm, and the total area of the two unshaded squares is 254.5cm sq. Find the total area of the two shaded right-angled triangles. Ans: 114.75cm sq

http://www.postimage.org/image.php?v=gxNVMm9

Hi KSP,

Here are my solutions.


MathsGuru

http://www.postimage.org/image.php?v=aVliTJ9

http://www.postimage.org/image.php?v=PqzMRX9

[mathsguru]

freakmum:

Mathsguru, how to solve this question?

If alan gives ben 6 sweets, the ratio of the number of sweets Alan will have to the number of sweets Ben will have is 2:5.
If Ben gives alan 8 sweets, the ratio of the number of sweets alan will have to the number of sweets ben will have is 1:2.
How many sweets did alan have at first?

Hi Freakmum,

Here's my solution. Hope my explanation is clear enough!


MathsGuru

http://www.postimage.org/image.php?v=TsLZvri

[mathsguru]

starlight1968sg:

Hi folks,

I need some help on p5 questions:

1) A greengrocer had 75 more apples than oranges at first. After selling 4/5 of the apples and 3/4 of the oranges, he had 285 fruits left.
(a) How many apples did he sell?
(b) What fraction of the fruits sold were oranges?
(ans: 540;5/11)

2) Ben and Caleb read a total of 60 books in November. In December, Ben read 15 fewer books than Caleb who read thrice as many books as he did in November. If both of them read a total of 90 books in December, how many books did Ben read in Nov and Dec?
(ans: 78 books)

MTIA.

Hi Starlight1968sg,

Here are my solutions. Hope they help!

In particular, for question 2, I couldn't get the answer \"78 books\" using the numbers stated in the question. I think the number \"15\" should be \"18\" right? (i.e. In December, Ben read 18 fewer books than Caleb....).

If I work out using \"15\", my answer will be 37.5 books in December and 42.5 books in November which are rather weird and total = 80 books.

Hence, my solution uses \"18\" to derive the answer. Nevertheless, the method used to solve this question is the same regardless of what the numbers are.


MathsGuru

http://www.postimage.org/image.php?v=gxPIaLJ

http://www.postimage.org/image.php?v=aVlFg0S

[starlight1968sg]

mathsguru:

Hi Starlight1968sg,

Here are my solutions. Hope they help!

In particular, for question 2, I couldn't get the answer \"78 books\" using the numbers stated in the question. I think the number \"15\" should be \"18\" right? (i.e. In December, Ben read 18 fewer books than Caleb....).

If I work out using \"15\", my answer will be 37.5 books in December and 42.5 books in November which are rather weird and total = 80 books.

Hence, my solution uses \"18\" to derive the answer. Nevertheless, the method used to solve this question is the same regardless of what the numbers are.


MathsGuru

Dear MathsGuru,
I am very sorry that the number is 18 instead of 15. Your models are very clear. Thanks so much for helping me.

[mathsguru]

starlight1968sg:

Dear MathsGuru,

I am very sorry that the number is 18 instead of 15. Your models are very clear. Thanks so much for helping me.

Hi Starlight1968sg,

No problem at all! Everyone makes typo errors once in a while, so no worries ya!

Glad tt u understand the solution.

Happy April Fool's Day,
MathsGuru

[firebird]

Dear mathsguru


Good morning.

Many thanks.
firebird