Ask Singapore Homework?

Upload a photo of a Singapore homework and someone will email you the solution for free.



Question

|
One Answer Below

Anyone can contribute an answer, even non-tutors.

Answer This Question
J
J

FORM 5 chevron_right Malaysia

Please help tq

Date Posted: 1 week ago
Views: 10
J
J
1 week ago
From 9 am to 11 am, 2 hours have passed.

2 hours = 120 min
120 min ÷ 15 min = 8
There are eight 15-min periods.

So the rumour passing started by the 4 villagers was done over 8 periods.


First 15 min, each of the 4 villagers told another 3 unique villagers. Then all of them each told another 3 unique villagers. So on and so forth.

Number of people who were told the rumour :

Before 9.00 am : 4

9.00 am to 9.15 am (first period) :
4 x 3 = 12

9.15 am to 9.30 am :
12 x 3 = 4 x 3 x 3 = 4 x 3^2
= 36

9.30 am to 9.45 am :
36 x 3 = 4 x 3^2 x 3
= 4 x 3^3 = 108

.
.
.

10.45 am to 11.00 am (8th period) :
4 x 3^8 = 26244





Realise that this works out to be a GP, with first term 4 and common ratio 3. Number of terms is 9.


So you can just use your formula for sum of GP.

S9

= 4(1 - 3^9) ÷ (1 - 3)
= 39364

See 1 Answer

done {{ upvoteCount }} Upvotes
clear {{ downvoteCount * -1 }} Downvotes
Derek Kua
Premium Tutor
Derek Kua's answer
6 answers (Tutor Details)
1st
hope this helps! (: