Short Answer: 18 minutes
Remark
The answer to this problem is less than the smallest time of the two people working together. that fact lets out C and D (38 minutes and 75 minutes). Now you have to choose 15 minutes and 18 minutes. There's a method. No guessing needed.
Givens
Let the time for Sophie = S
Let the time for Simon = M
Let the job to completion = 1
S = 45 minutes
M = 30 minutes
Step One
Convert minutes to hours.
45 minutes = 45 / 60 = 3/4 hour = 0.75 hour
30 minutes = 30 / 60 = 1/2 hour = 0.50 hour
Step Two
Set up the Equation
The formula is a form of job / hour.
Let the time = t that they both have to work
job = 1 in these problems.
1/S + 1/M = 1/t
1/0.75 + 1/0.5 = 1/t
Solve
1 ÷ 0.75 = 1.33333
1 ÷ 0.5 = 2
1.3333 + 2 = 3.33333
3.3333 = 1 / t Multlply both sides by t
3.3333*t = 1
t = 1 / 3.333333333
t = 0.3 of an hour
1 hour = 60 minutes
0.3 hours = x Cross Multiply
x = 60 * 0.3
x = 18 minutes
Answer working together it took them 18 minutes <<<<<
Answer:
23rd term of the arithmetic sequence is 118.
Step-by-step explanation:
In this question we have been given first term a1 = 8 and 9th term a9 = 48
we have to find the 23rd term of this arithmetic sequence.
Since in an arithmetic sequence
here a = first term
n = number of term
d = common difference
since 9th term a9 = 48
48 = 8 + (9-1)d
8d = 48 - 8 = 40
d = 40/8 = 5
Now 
= 8 + (23 -1)5 = 8 + 22×5 = 8 + 110 = 118
Therefore 23rd term of the sequence is 118.
