Tutor MathsGuru: Ask me for your burning Maths questions!

[MathIzzzFun]

wahwah:

Hi,

Need help in the following questions. Many thanks in advance.

Q1. One of the integers among 1,2,3,...,n is deleted. The average of the remaining (n-1) numbers is 602/17. Which number is deleted?

Q2. A student has taken examinations and 1 more examination is coming up. If he scores 100 in the upcoming examination, his overall average (of the n+1 examination) will be 90, if he scores 60 in the upcoming examination, his overall average will be 85. Find the number n.

Q3. The digits 3,4,5 and 7 can form 24 different four- digit numbers. Find the average of these 24 numbers.

Hi

Q1. 602/17 = 35 7/17 so the number of terms is around 70

Nearest multiple of 17 = 68

602/17 = 2408/68
Number of terms = 69

Sum of 1 to 69 = 69 x 35 = 2415
2415 - 2408 = 7

Number of terms = 69
Number deleted = 7

Q2. http://i55.tinypic.com/11kifef.jpg\">

Q3. Each digit will appear 6 times in each place value, so the average = (7777 + 5555 + 4444 + 3333 ) x 6 / 24

cheers.

[Herbie]

wah! all the n question are not Primary school maths right??

[CoffeeCat]

Herbie:

wah! all the n question are not Primary school maths right??

I m not wahwah but i can tell the questions can be found in primary school maths competitions =).

[wahwah]

Hi MathIzzzFun,

Thanks for the solution. But can you explain the model for Q2, my boy can’t understand it though he has been looking at it since Saturday.

[MathIzzzFun]

wahwah:

Hi MathIzzzFun,

Thanks for the solution. But can you explain the model for Q2, my boy can't understand it though he has been looking at it since Saturday.

Hi

I have added two more arrows in the model

http://i52.tinypic.com/21cuk8z.jpg\">

The blue arrow shows how the average marks increase when a new score (100) which is higher than the original average is added, and the red one shows how the average marks decrease after a new score which is lower than the original average mark is added.

When a new score of 100 is added, the overall average is 90. So the difference of (100-90) is divided among existing students to bring up the average.

Similarly, when a new score of 60 is added and the overall average becomes 85, in this case, the \"added\" marks of (85-60) for the new student is being contributed equally from the existing students.

Another way is look at is : imagine the original average mark as water level in a container, and adding a new \"tube\" with a higher water level so that the final water level in both the container and the tube reaches the same new level.

cheers.

[aiong]

Good morning, need help on the following math question, thank you


David has 4 times as many stickers as Ali. If David has 2160 more stickers than Ali.
How many stickers does they have altogether?

[sanie]

Can help with this qn. thanks


The ratio of $1 notes to $5 notes in Henry’s wallet is 2:3. If Henry exchanges 24 pieces for $5 notes for some $1 notes, he will have 12 times as many $1 notes as $5 notes. What is the total value of $1 notes and $5 notes in Henry’s wallet?

[wahwah]

Hi MathIzzzFun,

Thanks so much for the explanation. My boy understands now.

[amirtha]

Dear Maths Guru


Could you pls help to solve the below P6 question.


http://i56.tinypic.com/33m0nm1.jpg\">


thks

[MathIzzzFun]

wahwah:

Hi MathIzzzFun,

Thanks so much for the explanation. My boy understands now.

hi wahwah,

you are welcome :lol:

cheers.