ElectricPavlov

4   is ONE    ( counting up to 1024)   maybe the ONLY one?

x

x^2

x^2 +10

x^2 + 10 -3 = x^2 + 7

+7       7^2 = 49      sqrt 49 = 7        This is kinda silly.....

5 x 45 = 225   (sum would be 5175)

(amazing is correct...I assumed she started with '5')

.4 (75) + x(25) = .5 (100)

x = .8    or 80%

You left out the numbers! 

You have to take into account the TIME at each speed.....the TIME to travel the same distance will be LONGER for 40 m/hr vs 60 m/hr so the AVERAGE will be weighted more toward the 40 m/hr ...

40 x t₁ = d    d/40 = t1

60 x t₂ = d    d/60 = t2

2d/avg = t1 + t2 = d/40 + d/60

2d/avg = (3d+2d)/120

2/avg = 5/120

avg/2 = 120/5

avg = 240/5 = 48 m/hr

I initially read the Q incorrectly.....d'oh! 

Here is a graph:

99/100   are managers (99%)

.98 x   =  .98 (100-x)

.98 x = 98 - .98x

1.96 x = 98

x = 50

If 50 leave the room then there will be  49 managers in the room of 50 people = 98%   (as rasberry found! )

You're welcome!   I hope it is clearer to you now ......