Let c represent the speed of the current.
time = distance / speed
total time = time going upriver + time going downriver
2 2/3 = 6/(9 -c) + 6/c
(8/3)(c)(9 -c) = 6c +6(9 -c)
(8/3)c^2 -24c +54 = 0
c = (24 ± √((-24)^2 -4(8/3)(54)))/(2*8/3)
.. = (3/16)(24)
c = 4.5
The speed of the river's current is 4.5 km/h.
It is (c+d)
you can basically use FOIL (first,outside,inside,last) to solve this.
you know the first term of the factor has to be C because of the c^2
the second then has to be D because you haven't seen D in the factor yet and it is in the equation.
then you know from the equation that the terms with D are not negative so D isn't negative so you have form the information above (c+d)
I believe they call it a recurring number, for example, infinity is a recurring number.
A- 98+89+123=310 (boys)
A-102+105+117=324 (girls)
B-324-310=14 I found my answer by subtracting the girls from the boys and I got 14
C-They will need to hire 24 more teachers because if you add the students together you will get 644 then you divide it by 20 and you get 32 but since they already have 8 teachers you would just subtract 8 from 32 wich you get 24