(6 + 3) + 21 = 6 + (3 + 21)
It's an ASSOCIATIVE PROPERTY
(a + b) + c = a + (b + c)
X - speed of the current
40+x - speed with current
40-x - speed against current
t-time
(40+x)*t=100
(40-x)*t=60
40t+xt=100
<span> + 40t-xt = 60
</span> 80t =160
t = 2
40t+xt=100,
40*2+2x=100
80+2x=100
2x=100-80
2x=20
x=10 mi/h
10 mi/h speed of the current.
The rule is x+1.05 because every number goes up 1.05
I hope I've helped!
Less than 12: 11 numbers
probability of getting less than 12: 11/100