Ask Singapore Homework?
Upload a photo of a Singapore homework and someone will email you the solution for free.
Question
junior college 2 | H2 Maths
One Answer Below
Anyone can contribute an answer, even non-tutors.
1. I would like to ask but how fo you find the probability that the sum of 2 cards is smaller than 5 to be 1/9? when I tried this question my answer was 6/36=1/6
How would you answer the part where they ask for "at least one draw" has a value of less than 5?
Thank you in advance.
total outcome = 9x8 = 72
for sum of 5 or less, possible combinations are ...
12,13,14,21,23,31,32,41 (8 combinations)
P(sum 5 or less) = 8/72 = 1/9
if it is draw 1 card, replace, draw another card,
it would be "with replacement", then we can consider the combinations of 11 & 22
for "with replacement",
P(sum 5 or less) = 10/81
so cannot figure out how you can get 1/6
(2)(ii)
for "at least one draw", need to consider 3 cases ...
case 1: 5 or less on BOTH draws
case 2: 5 or less on 1st draw but not on 2nd
case 3: 5 or less on 2nd draw but not on 1st
P(5 on less on at least one draw)
= 1/9 x 1/9 + 1/9 x 8/9 + 8/9 x 1/9 = 17/81
alternatively, use complement method
P(5 or less on at least one draw)
= 1 - P(5 or less on 0 draw)
= 1 - 8/9 x 8/9 = 17/81
Answers :
A /B = 1/9
CD/EF = 29/12
G/HI = 1/81
JK/LM = 17/81
I thought since the order was not important I used the combination formula instead of the permutation formula.
I did 9!/[2!*(9-2)!] and got 36.
Also, how did you make sense of CD and EF?
12 is same as 21,
13 is same as 31
14 is same as 41
23 is same as 32
so you have 4 combinations
P(sum 5 or less) = 4/36 = 1/9
note that ...
sum 3 possible only with cards 1&2 ;
probability = 1/36
sum 4 possible only with cards 1&3 ;
probability = 1/36
sum 5 possible only with cards 1&4, and 2&3 ; probability = 2/36
summary ...
sum | score | probability
3 | 10-3 = 7 | 1/36
4 | 10-4 = 6 | 1/36
5 | 10-5 = 5 | 2/36
6 to 17 | 2 | 32/36
expected score
= summation(score x probability)
= 7 x 1/36 + 6 x 1/36 + 5 x 2/36 + 2 x 32/36
= 87/36
= 29/12
See 1 Answer