Q&A - PSLE Math

[student101]

Thank you very much. How fast you solved the problem which i burnt my head for few hours without success. Thank you once again.

[stary]

student101:

Thank you very much. How fast you solved the problem which i burnt my head for few hours without success. Thank you once again.

No problem!

[stary]

Hi all,


Have two questions to seek for help:-

1) Tim's present age is thrice Susan's age some years ago. Conversely, Susan's
present age is Tim's age the same number of years ago. Given that the sum
of their present ages is 30 years, how old is Tim now?

2) When Ken's age was twice Bob's age, Mark's age was 30. When Mark's age
was twice Ken's age, Bob's age was 21. Given that Mark was the oldest
among the three persons, find Bob's age when Mark was 62 years old.

Thanks in advance :?

[raghupavithra]

gordon, kenneth and leon spent their money in the ratio 3:4:7 last month.this month,gordon’s expenditure increased while kenneth’s expenditure decreased. If gorden and kenneth spent the same amount this month while leon spent $350 more than gorden, what was the total expenditure of the three boys last month?


how to solve this? pls help me

[MathIzzzFun]

stary:

Hi all,


Have two questions to seek for help:-

1) Tim's present age is thrice Susan's age some years ago. Conversely, Susan's
present age is Tim's age the same number of years ago. Given that the sum
of their present ages is 30 years, how old is Tim now?

2) When Ken's age was twice Bob's age, Mark's age was 30. When Mark's age
was twice Ken's age, Bob's age was 21. Given that Mark was the oldest
among the three persons, find Bob's age when Mark was 62 years old.

Thanks in advance :?

Hi

1)
Name....Age Some Years ago..……. Age Now
Susan…… [1unit] …………..…......[1unit][age gap][age gap]
Tim ……….[1unit][age gap]..…… [1unit][1unit][1unit]

So, comparing the ages NOW,
[age gap] = [1unit]

Age Now = 5 units = 30, 1 unit = 6

Age now:
Susan = 6+6 = 12 years old
Tim = 3 x 6 = 18 years old


2) question is same as this which was discussed some time ago - http://www.flickr.com/photos/62167097@N02/5679985631/in/photostream

cheers.

[htn]

Best wishes[/quote]

After 70 blue marbles removed,
Ratio of blue marbles : white marbles = 3u : 4u

If 112 white marbles are removed, then blue marbles : white marbles
= 3u + 70 : 4u – 112


an alternative approach …

After 70 blue marbles removed,
Ratio of blue marbles : white marbles = 3u : 4u

If 112 white marbles are removed, then blue marbles : white marbles
= 3u + 70 : 4u – 112
= 8 : 7

Cross-multiply- 7 x (3u + 70) = 8 x (4u-112)
21u + 490 = 32u – 896
11u = 1386, 1u = 126

Number of blue marbles = 3u + 70 = 3 x 126 + 70 = 378 + 70 = 448
Number of white marbles = 4u = 4 x 126 = 504

When 48 more blue marbles are added, number of blue marbles = 448 + 48 = 496
Total number of marbles = 48 + 448 + 504 = 1000

Percentage of blue marbles = 496/1000 = 49.6%

cheers.[/quote]
Hi, why after If 70 blue marbles removed is 3u + 70
after If 112 white marbles are removed is 4u - 112

Thanks

[MathIzzzFun]

htn:

Best wishes

After 70 blue marbles removed,
Ratio of blue marbles : white marbles = 3u : 4u

If 112 white marbles are removed, then blue marbles : white marbles
= 3u + 70 : 4u – 112


an alternative approach ..

After 70 blue marbles removed,
Ratio of blue marbles : white marbles = 3u : 4u

If 112 white marbles are removed, then blue marbles : white marbles
= 3u + 70 : 4u – 112
= 8 : 7

Cross-multiply- 7 x (3u + 70) = 8 x (4u-112)
21u + 490 = 32u – 896
11u = 1386, 1u = 126

Number of blue marbles = 3u + 70 = 3 x 126 + 70 = 378 + 70 = 448
Number of white marbles = 4u = 4 x 126 = 504

When 48 more blue marbles are added, number of blue marbles = 448 + 48 = 496
Total number of marbles = 48 + 448 + 504 = 1000

Percentage of blue marbles = 496/1000 = 49.6%

cheers.[/quote]
Hi, why after If 70 blue marbles removed is 3u + 70
after If 112 white marbles are removed is 4u - 112

Thanks[/quote]

Hi

After 70 blue marbles removed, ratio of blue: red = 3u : 4u
so before the 70 blue marbles is removed, number of blue marbles = 3u + 70 = number of blue marbles at first.

So at first, number of blue : red = 3u + 70 : 4u
Remove 112 red marbles, and the ratio becomes 3u+70 : 4u-112

cheers.

[htn]

Hi, need help


Mrs Hoon made some cookies to sell. 3/4 of them were chocolate cookies and the rest were almond cookies. After selling 210 almond cookies and 5/6 of the chocolate cookies, she had 1/5 of the cookies left.

How many cookies did Mrs Hoon sell?
Thanks

[htn]

MathIzzzFun:

htn:

Best wishes

After 70 blue marbles removed,
Ratio of blue marbles : white marbles = 3u : 4u

If 112 white marbles are removed, then blue marbles : white marbles
= 3u + 70 : 4u – 112


an alternative approach ..

After 70 blue marbles removed,
Ratio of blue marbles : white marbles = 3u : 4u

If 112 white marbles are removed, then blue marbles : white marbles
= 3u + 70 : 4u – 112
= 8 : 7

Cross-multiply- 7 x (3u + 70) = 8 x (4u-112)
21u + 490 = 32u – 896
11u = 1386, 1u = 126

Number of blue marbles = 3u + 70 = 3 x 126 + 70 = 378 + 70 = 448
Number of white marbles = 4u = 4 x 126 = 504

When 48 more blue marbles are added, number of blue marbles = 448 + 48 = 496
Total number of marbles = 48 + 448 + 504 = 1000

Percentage of blue marbles = 496/1000 = 49.6%

cheers.

Hi, why after If 70 blue marbles removed is 3u + 70
after If 112 white marbles are removed is 4u - 112

Thanks[/quote]

Hi

After 70 blue marbles removed, ratio of blue: red = 3u : 4u
so before the 70 blue marbles is removed, number of blue marbles = 3u + 70 = number of blue marbles at first.

So at first, number of blue : red = 3u + 70 : 4u
Remove 112 red marbles, and the ratio becomes 3u+70 : 4u-112

cheers.[/quote]


Thanks

[MathIzzzFun]

htn:

Hi, need help


Mrs Hoon made some cookies to sell. 3/4 of them were chocolate cookies and the rest were almond cookies. After selling 210 almond cookies and 5/6 of the chocolate cookies, she had 1/5 of the cookies left.

How many cookies did Mrs Hoon sell?
Thanks

Hi

ratio of choc cookies : almond cookies
= 3:1
= 30u : 10u --> total cookies = 40u

After selling 5/6 choc cookies and 210 almond cookies, number of cookies left ;
choc cookies = 1/6 x 30u = 5u
almond cookies = 10u-210
total left = 5u + 10u -210= 15u - 210 = 1/5 of number at first = 1/5 x 40u = 8u
15u - 210 = 8u
7u = 210, 1u = 30
Total cookies sold = 4/5 x 40u = 4/5 x 40 x 30 = 960

cheers.