Q&A - P3 Math

[Lilac66]

buds:

Easiest method to solve this one?


A snail climbed 1cm up a wall in Day 1,
2cm in Day 2, 3cm in Day 3 and so on..

Each day, it climbed 1cm more than it did
the previous day. How many days did the
snail take to climb 21cm?

My son tried to solve it this way and wanted to share it: 1st,21-1=20,2nd,20-2=18, 3rd,18-3=15,4th,15-4=11,5th,11-5=6,6th day,6-6=0 It's another way of listing, I guess.

[shirley.020816tamzil]

Hi, have a question here:


Mary had some money. She spent $38.15 on books. Her father gave her another $75 and she had a total of $155.35 in the end. How much did Sharleen have at first?

DS worked it to be $38.15+$75+$155.35=$268.50.
But I disagree, looking at the 3rd sentence, I think that the $75 is part of the $155.35 in the end, so it should be just $38.15+$155.35=$193.50.
DS argued that then $75 is not used at all which he thinks should not be the case (I sorta told him bfore that every number is important in maths problem :oops: )

Anyone can help us? Thank in adv.

[Dharma]

shirley.tamzil:

Hi, have a question here:


Mary had some money. She spent $38.15 on books. Her father gave her another $75 and she had a total of $155.35 in the end. How much did Sharleen have at first?

DS worked it to be $38.15+$75+$155.35=$268.50.
But I disagree, looking at the 3rd sentence, I think that the $75 is part of the $155.35 in the end, so it should be just $38.15+$155.35=$193.50.
DS argued that then $75 is not used at all which he thinks should not be the case (I sorta told him bfore that every number is important in maths problem :oops: )

Anyone can help us? Thank in adv.

Just need to work backwards
Amt Sharleen had at first
=$155.35 - $75 + $38.15
= $ 118.50

[shirley.020816tamzil]

Dharma:

Just need to work backwards

Amt Sharleen had at first
=$155.35 - $75 + $38.15
= $ 118.50

Oh I see, both of us are wrong. Thanks for your enlightenment... :lol:

[yeonee]

Hi, why we have to divide by 2 for this equation?



quote=\"Dharma\"]

Muffins:

Hi Dharma.

Sorry to be a buzzkill, but the actual question was 21 cm, not 210 cm....

Hi Muffins,

To climb 21cm

N x (N + 1) / 2 = 21

N x (N + 1) = 42
6 x 7 = 42
N = 6 days

By using 210cm I was trying to show that it will be easier to solve the problem by finding a pattern. The listing method will
be just too long.[/quote]

[Dharma]

yeonee:

Hi, why we have to divide by 2 for this equation?



quote=\"Dharma\"]

Muffins:

Hi Dharma.

Sorry to be a buzzkill, but the actual question was 21 cm, not 210 cm....

Hi Muffins,

To climb 21cm

N x (N + 1) / 2 = 21

N x (N + 1) = 42
6 x 7 = 42
N = 6 days

By using 210cm I was trying to show that it will be easier to solve the problem by finding a pattern. The listing method will
be just too long.

[/quote]

Hi yeonee,

Hope the link below may be useful.

http://home.covad.net/~bfjacobs/Student_Info/Math_Fun/Patterns/Triangular_Nos/lesson.html

[SPI]

Need help for this question. Thanks.


Linda used 2/3m of string to tie a pile of books and had 7/12m of string left. What was the original lenght of string she had at first?


Sorry post wrong place. Should be at P3/P4 Maths section.

[SPI]

Need help for this question. Thanks.


Linda used 2/3m of string to tie a pile of books and had 7/12m of string left. What was the original lenght of string she had at first?

[Brenda10]

SPI:

Need help for this question. Thanks.


Linda used 2/3m of string to tie a pile of books and had 7/12m of string left. What was the original lenght of string she had at first?

HI, the answer should be 1 1/4m

2/3 + 7/12 (make the base same to 12, that will be 2 x 4 and 3 x 4)
8/12 + 7/12 = 15/12
15/12 = 1 1/4

[yeonee]

Hi, I have one question:-


John had 4 times as much money as Jessie. After John received$240 and Jessie received $180, John now has twice as much money as Jessie. How much did they have altogether at first?