forestcadee:

mum2BG:

Appreciate help on the below Average question, looks simple but can't figure out why need to take original price minus new average price,


Sam bought some pencils at an average price of $5 each. If he bought another pencil for $17, the average price would be $7. How many pencils did he buy altogether?

Hi, my dd's answer is 5 because it is the fact that Sam only bought 5 pencils. The 6th one is quoted under \"If\",so it isn't true that the 6 th pencil is bought.

Yes, your dd right. My mistake for not minus-ing 1.

mum2BG:

Appreciate help on the below Average question, looks simple but can't figure out why need to take original price minus new average price,


Sam bought some pencils at an average price of $5 each. If he bought another pencil for $17, the average price would be $7. How many pencils did he buy altogether?

http://i59.tinypic.com/25ajm1j.jpg\">

Short of using Algebra.... we need to analyse the question.

Some pencils will be >= $5 and some will be <=$5.
When we talk about average, we can think of each pencil having the same price.

The new average price is an increase of $2 from the old average price. Each pencil now costs $2 more.
Where do all these $2s come from? They have to come from the difference between the price of the new pencil ($17) and the old average price ($5). In other words, you can distribute $2s out from this difference to each pencil until each is now “topped-up” to the new average price of $7.

The number of $2s in that difference will be the total number of pencils bought.
From the diagram, the number of pencils bought is ($17-$5)/$2 = 6.

I didn’t ask the question. I’m only responding because you asked if it’s correct.

Mathagog:

KiasuAhMa:

Hi please answer the question below

It is p5 average

After a test, Peter and his friends calculated their average score.They found that if Peter got 14 more marks than what he did,they would have an average score of 88 marks. If Peter got 10 fewer marks than he did,their average score would become 85 marks. How many friends did Peter have?

Pls show workings too,thanks

Solution:

Let 'N' be the unknown number of children including Peter whose average is being calculated.

http://i57.tinypic.com/33mu0r9.jpg\">

From the model diagram we see that,

The total marks causing the change in average from 88 to 85 = 10+14=24.
Total marks of all children if Peter had got 14 more marks = 88xN
Total marks of all children if Peter had got 10 less marks = 85xN

Therefore,

Difference in totals,

88xN-85xN = 24
3xN = 24
N =24/3
N=8

Ans: Peter has 7 friends

http://i62.tinypic.com/mwwpso.jpg\">

ttlkbs:

Help pls:


http://i57.tinypic.com/21e68lj.jpg\">

http://i58.tinypic.com/27yo2l1.jpg\">

belnanna:

Hi all,


THis question has been asked in the forum before..However, there wasnt a detailed explanation to this question... Would some kind soul please help to solve this ..THanks in advance!

If Kenny gives 18 marbles to Andrew, he will have thrice as many marbles as Andrew. If Andrew gives 12 marbles to kenny, he will have 1/9 of the number of marbles that kenny has. How many marbles does Kenny have at first?

http://i60.tinypic.com/25ja6a1.jpg\">

TheSolver:

NerdyMath:

Ethan's daily allowance is $4 more than Lucy's

Ethan spends 4 times as much as Lucy each day.
Ethan takes 5 days to save $10 while Licy takes 4 days to save the same amount. How much does Ethan spend per day?

$10/5=$2
$10/4=$2.50
$2.50-$2=$0.50
$0.50+$4=$4.50
4-1=3
$4.50/3=$1.50
$1.50*4=$6
Ans: $6

Yes. $6 is correct.

http://i57.tinypic.com/301fzf7.jpg\">

ozora:

need someone to check whether my answer is correct for the question.


2 men take r minutes to dig a trench. How many men will it take to dig 2 trenches in 1/2h?

trench : time : men
1 : r min : 2
1 : 1 min : 2r
1 : 30 min : 2 r /30
1 : 30min : r/15
2 : 30min : 2r/15

ans 2r/15 men

http://i61.tinypic.com/15cmuxs.jpg\">

angel:

60% of the number of marbles in box A is equal to 75% of the number of marbles in box B. Box C has half the number of marbles in box A. Box B has 60 marbles more than that in box C.


a) How many marbles are there in box A?
b) How many marbles must be transferred from box B to box C so that box C has 90% of the number of marbles in box A?

http://i58.tinypic.com/2mhiwxv.jpg\">

alfretztay:

numeric:

[quote=\"vaun\"]P5 Math Mid year Exam 2010 - Question 17


There are 42 pupils in each of the classes. primary 5A and primary 5B. The ratio of the no. of boys in 5A to the no. of boys in 5B was 3:4. The ratio of the no. of girls in 5A to the no. of girls in 5B was 4:3. There were 56 boys altogether in both classes. What was the ratio of boys in 5A to the no. of girls in in 5B.

My steps :
......5A (42) : 5B(42)

Boy Ratio 3 : 4 => Total 56 boys
Girl Ratio 4 : 3 => total shall be 84-56=28
-----------------------------------------------------
If so, the no of boy in 5A and 5B shall be
........... 24 : 32
but if so, the no. of girls in 5A and 5B shall be
........... 16 : 12
But if so, the no. of pupil is 5A will only be 24+16.....
The standard answer is 1:1.

Can anyone advise ? :?

http://i58.tinypic.com/25jzgbb.jpg\">

I believe that the sentence 'There were 56 boys altogether in both classes.' ought to be deleted in order to arrive at the standard answer. Alternatively, '56' could be changed to 42.[/quote]Thanks for highlighting. I take the ratios as they are, and ignore the numbers since both classes have the same number of pupils.

Nothing wrong with your thinking
alfretztay is right.
The question has a contradiction in it.
If there are really 56 boys in both classes and the boy ratio is 3:4, then
5A: 8 boys, 8 boys, 8 boys, 18 girls
5B: 8 boys, 8 boys, 8 boys, 8 boys, 10 girls

18 girls in 5A: 10 girls in 5B won't give a 4:3 ratio.