Tutor MathsGuru: Ask me for your burning Maths questions!

[rain29]

Hi Pixiedust,


Thanks for your help.

[jieheng]

wkong:

Hi All,


Need help for this question:

A train, 200m long, travelled through a tunnel at an average speed of 20m/s. The whole train took 2 min 30s to pass through the tunnel completely. Find the length of the tunnel in kilometres.

Thanks,
wkong

2 min 30 s = 150 s

Total distance travelled by the train = 20 * 150 = 3000 m

Length of tunnel = 3000 - 200 = 2800 m = 2.8 km (Ans)

[HVR]

Appreciate it if anyone can help. TIA


Roger is 30 yrs old when James is twice the age of John. When John is 21 yrs old, Roger is twice the age of James. Given that Roger is the oldest of them, find john’s age when Roger is 62 yrs old.

[jieheng]

HVR:

Appreciate it if anyone can help. TIA


Roger is 30 yrs old when James is twice the age of John. When John is 21 yrs old, Roger is twice the age of James. Given that Roger is the oldest of them, find john's age when Roger is 62 yrs old.

When Roger is 30 yrs old

Roger [ ][ ] [------] = 30 yrs
James [ ] [ ]
. John [ ]

[------] denotes the the difference of age between Roger and James and it will be the same throughout their lives

[ ] denotes the the difference of age between James and John and it will be the same throughout their lives . In this case , the ages of [ ]and[ ] are the same

When John is 21 yrs old

John [ 21 ]
James [ 21 ][ ]
Roger [ 21 ][ ][ 21 ][ ] as Roger is twice the age of James


[------] = [ 21 ][ ]


[ ][ ] [------] = 30 yrs

[ ][ ][ 21 ][ ] = 30 yrs

[ ] = [ ] = (30-21) / 3 = 3

When John is 3 yrs old , James is = 3 + 3 = 6 yrs old and Roger is 30 yrs old .

Roger is (30-3) = 27 yrs older than John .

When Roger is 62 yrs old ,

John is = (62-27) = 35 yrs old (Ans)

[wahwah]

HI,

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

A worker takes 9 hrs to build a wall while another worker takes 10 hr to build the same wall. When both workers work together, they sometimes stop for a chat and they lay 10 bricks fewer per hour than their total if they had worked seperately. If the two workers take 5 hours to build the wall together, how many bricks are needed for the wall?

I have six coins- three 5 cents coins and three 10 cents coins. I place two coins in each of three boxes labeled 10 cents, 15cents and 20cents in such a way that these are not the respective values of coins inside. What is the least number of coins you would have to remove, and from which box or boxes, so as to determine which coins are in which boxes? Write your explanation clearly.

[HVR]

jieheng:

HVR:

Appreciate it if anyone can help. TIA


Roger is 30 yrs old when James is twice the age of John. When John is 21 yrs old, Roger is twice the age of James. Given that Roger is the oldest of them, find john's age when Roger is 62 yrs old.

When Roger is 30 yrs old

Roger [ ][ ] [------] = 30 yrs
James [ ] [ ]
. John [ ]

[------] denotes the the difference of age between Roger and James and it will be the same throughout their lives

[ ] denotes the the difference of age between James and John and it will be the same throughout their lives . In this case , the ages of [ ]and[ ] are the same

When John is 21 yrs old

John [ 21 ]
James [ 21 ][ ]
Roger [ 21 ][ ][ 21 ][ ] as Roger is twice the age of James


[------] = [ 21 ][ ]


[ ][ ] [------] = 30 yrs

[ ][ ][ 21 ][ ] = 30 yrs

[ ] = [ ] = (30-21) / 3 = 3

When John is 3 yrs old , James is = 3 + 3 = 6 yrs old and Roger is 30 yrs old .

Roger is (30-3) = 27 yrs older than John .

When Roger is 62 yrs old ,

John is = (62-27) = 35 yrs old (Ans)

Now I can explain to my kid. Thank you very much

[Vanilla Cake]

wahwah:

A worker takes 9 hrs to build a wall while another worker takes 10 hr to build the same wall. When both workers work together, they sometimes stop for a chat and they lay 10 bricks fewer per hour than their total if they had worked seperately. If the two workers take 5 hours to build the wall together, how many bricks are needed for the wall?

In 1 hour, worker A builds 1/9 of a wall
In 1 hour, worker B builds 1/10 of a wall
In 1 hour, both workers work together, sometimes stop for a chat and they lay 10 bricks fewer than the total means (1/9+1/10)of a wall-10
= 19/90 of a wall - 10 -> case 1

Given that the 2 workers take 5 hours to build a wall together means that 5 hours = 1 wall
1 hour = 1/5 of a wall -> case 2

Since case 1 = case 2 as they are the rate of building a wall for both workers A and B working together means
19/90 of a wall - 10 = 1/5 of a wall
(19/90-1/5) of a wall = 10
(19/90-18/90) of a wall = 10
1/90 of a wall = 10
A wall = 10x90 = 900

Number of bricks needed for the wall = 900.

[jieheng]

HVR:

Now I can explain to my kid. Thank you very much

Hi HVR ,

You are welcome .

Regards,

[MathIzzzFun]

wahwah:

HI,

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

A worker takes 9 hrs to build a wall while another worker takes 10 hr to build the same wall. When both workers work together, they sometimes stop for a chat and they lay 10 bricks fewer per hour than their total if they had worked seperately. If the two workers take 5 hours to build the wall together, how many bricks are needed for the wall?

I have six coins- three 5 cents coins and three 10 cents coins. I place two coins in each of three boxes labeled 10 cents, 15cents and 20cents in such a way that these are not the respective values of coins inside. What is the least number of coins you would have to remove, and from which box or boxes, so as to determine which coins are in which boxes? Write your explanation clearly.

Q1.
When the workers work separately,
in 1 hour, they would build 1/9 + 1/10 = 19/90 of the wall

When they work together, they lay 10 less bricks per hour and therefore could finish the wall in 5 hours ie they could complete only 1/5 of the wall in 1 hour

So 19/90 of wall - 10 bricks = 1/5 of wall

1/90 (= 19/90 - 1/5) of wall = 10 bricks ==> Full wall = 90 x 10 bricks = 900 bricks.

Q2.
There are only two ways to place the coins in the 3 boxes such that the value of coins in each box will not be the same as the label on the box.

Combination 1 - 10 cents box (5cents + 10cents), 15 cents box (10 cents + 10 cents), 20 cents box (5 cents + 5 cents)

Combination 2 - 10 cents box (10 cents + 10 cents), 15 cents box (5 cents + 5 cents), 20 cents box (5 cents + 10 cents)

So by removing one coin from the 15 cents box, one will be able to determine which coins are in which box. If it is a 5-cent coin > combination 2. If it is a 10-cent coin > combination 1.

cheers.

[SaPan]

Dear uncles/aunties,

pls help me with this question.

A group of children met for a table tennis game. Each child played with everyone else. Lisa played with thrice as many girls as boys. Bob played with 4 times as many girls as boys.

a. how many children were there altogether?
b. were there more boys or girls? how many more?

thank you in advance