The Malthouse Charity Run is a 5 kilometre race. The time taken for each runner to complete the race was recorded. The data was found to be normally distributed with a mean time of 28 minutes and a standard deviation of 5 minutes.
A runner who completed the race is chosen at random.
Write down the probability that the runner completed the race in more than 28 minutes.
3b. [2 marks]
Calculate the probability that the runner completed the race in less than 26 minutes.
3c. [3 marks]
It is known that 20% of the runners took more than 28 minutes and less than minutes to complete the race.
Find the value of .

Ok here we go ..there are plenty of ways to solve such math problems but we will go for the smartest and easiest ..5x+2y=7  -2x+6y=9we rearrange them into the following ..by multiplying the 1st equation by 2 it becomes 10x + 4y = 14we rearrange it and so it becomes 10x = 14 - 4yas for the second equation we multiply it by 5 and rearrange it so it becomes as to the following ..-10x + 30y = 45rearranging so 10x = 30y -45now 10x equals both 14 - 4y and 30y -45so   14 - 4y = 30y -4531 = 26yy= 31/26 = 1.19 or around 1.2so by now we can calculate x easily as  -2x+6y=9so 2x = 6y -9 = 6 * 31/26 - 9 = -1.84  then x = - 0.92 or around -0.9best luck!

8x - 61 = 17add 8x = 88x = 11 (cannot be proven)4(3(7) - 8) = 524(21 - 8) = 5284 - 32 = 52 (proven)