Ask Singapore Homework?
Upload a photo of a Singapore homework and someone will email you the solution for free.
Question
Primary 3 | Maths
2 Answers Below
Anyone can contribute an answer, even non-tutors.
I don’t understand why the answer is 45 instead of 81. Isn’t each girl say to 9 other girls hello one time each. Hence 9x9= 81?
Date Posted: 2 years ago
Views: 711
My answer is 90.
Each of the 10 girls says hello to 9 other people, so it’s 10 x 9 = 90.
There are 45 “pairs” of hellos because there are 45 meetings altogether, but there are 90 hellos in total.
Each of the 10 girls says hello to 9 other people, so it’s 10 x 9 = 90.
There are 45 “pairs” of hellos because there are 45 meetings altogether, but there are 90 hellos in total.
But the answer in the book is 45. Not 90.
In other words…I disagree with the answer given.
Not all answers in textbooks are always correct. They are answers given by publishers.
Not all answers in textbooks are always correct. They are answers given by publishers.
Someone else have 45. But I don’t understand his table.
Ok, it goes this way. Wait for me to update this list.
Suppose you line up the 10 people. How the meetings can go is like this.
1st —> meets 2nd, 3rd, 4th, 5th, 6th, 7th, 8th, 9th and 10th
2nd —> meets 3rd, 4th, 5th, 6th, 7th, 8th, 9th and 10th (the 2nd person has already met the first)
3rd —> meets 4th, 5th, 6th, 7th, 8th, 9th, 10th (the 3rd person has already met the first and second)
4th —> meets 5th, 6th, 7th, 8th, 9th, 10th
…
9th —> meets 10th
The total number of meetings
= 9 + 8 + 7 + 6 + 5 + 4 + 3 + 2 + 1
= 45
But in each meeting, two hellos are exchanged.
For a total of 90 hellos.
Suppose you line up the 10 people. How the meetings can go is like this.
1st —> meets 2nd, 3rd, 4th, 5th, 6th, 7th, 8th, 9th and 10th
2nd —> meets 3rd, 4th, 5th, 6th, 7th, 8th, 9th and 10th (the 2nd person has already met the first)
3rd —> meets 4th, 5th, 6th, 7th, 8th, 9th, 10th (the 3rd person has already met the first and second)
4th —> meets 5th, 6th, 7th, 8th, 9th, 10th
…
9th —> meets 10th
The total number of meetings
= 9 + 8 + 7 + 6 + 5 + 4 + 3 + 2 + 1
= 45
But in each meeting, two hellos are exchanged.
For a total of 90 hellos.
What does the table mean in duplication? Do you understand his solution?
The “hello” in the tutor’s example is actually the “meeting” which I was talking about.
The question assumes that one “hello” means one “meeting”.
If we consider from the “meeting” point of view, there is no difference between “first person meeting the second person” and “the second person meeting the first person”. In this case, there would be double-counting as indicated in the tutor’s table.
The question assumes that one “hello” means one “meeting”.
If we consider from the “meeting” point of view, there is no difference between “first person meeting the second person” and “the second person meeting the first person”. In this case, there would be double-counting as indicated in the tutor’s table.
I think that the “each other” in the question is ambiguous in the meaning.
I would personally feel that saying hello to each other means that two hellos are exchanged together between two people.
In a normal context, both people will say hello correct?
Which is how I obtained 90.
I would personally feel that saying hello to each other means that two hellos are exchanged together between two people.
In a normal context, both people will say hello correct?
Which is how I obtained 90.
Okay. I think I may get it. Thank you.
Instead of say Hello, it should use shake-hand to each other....
See 2 Answers
What does NA mean in the table mean?
What is the meaning of duplications? I don’t understand. Can you give an example?
If 1 said hello to 2. It is considered they have said hello to each other and we treat 2 said hello to 1 as a duplication.
The working in the book is 9+8+7+6+ 5+4+3+2+1 = 45. can you explain the working without the use of the table? The table is confusing.
done
{{ upvoteCount }} Upvotes
clear
{{ downvoteCount * -1 }} Downvotes
Hope this helps
Date Posted:
2 years ago
I don’t understand the diagram. Can you explain it?
Look at white line...
Person number 1 will say HELLO to person number 2
Person number 3
Person number 4
Person number 5
.
.
.
.
Person number 10
Total HELLO = 9
THEN person number say Hello to
Person number 3
Person number 4
Person number 5
.
.
.
.
Person number 10
Total hello = 8....
And so on...
Therefore, total all hello
9+8+7+6+5+4+3+2+1 = 45
Person number 1 will say HELLO to person number 2
Person number 3
Person number 4
Person number 5
.
.
.
.
Person number 10
Total HELLO = 9
THEN person number say Hello to
Person number 3
Person number 4
Person number 5
.
.
.
.
Person number 10
Total hello = 8....
And so on...
Therefore, total all hello
9+8+7+6+5+4+3+2+1 = 45
Why is it not each of them say hello to 9 people? Instead of 9 times, 8 times, 7 times, Etc?
Ah.. when person number 1 say hello to person number 2...
Person number 2 will not say Hello again to person number 1...
Because 1-2 or 2-1 is already done
Person number 2 will not say Hello again to person number 1...
Because 1-2 or 2-1 is already done
When they met and said HELLO to each other, meaning 1 met 2, both say HELLO, count as one.
Anyway, for his question not very clear about number of HELLO said.
Normally, question will use shake hand to each other once when they meet.
Anyway, for his question not very clear about number of HELLO said.
Normally, question will use shake hand to each other once when they meet.
360 Tutoring Program