a boat is going 144 miles upstream on a river. the speed of the boat in still water is 60 miles per hour. the speed of the river current is 80% less than the speed of the boat in still water. how long does the journey take?( in hours)

Let  b  =  rate of the boat.

Let  r  =  rate of the river.

The rate going downstream is  b + r.

The rate going upstream is  b - r.

rate x time  =  distance

4(b + r)  =  144     --->     b + r  =  36     [divide both sides by 4]

9(b - r)  =  144      --->     b - r  =  16      [divide both sides by 9]

Add town:                          2b  =  52  

Divide by :                           b  =  26  mi/hr

                                           r  =  10  mi/hr

Step-by-step explanation:

step-by-step explanation:

the original amount doesn't ''re just looking for the time it takes for 1/2 of the substance to we have

(1/2) =)     take the ln   of both sides

ln (1/2)   = )   and we can write

ln(1/2) = ) lne     and lne   = 1     so we have

ln(1/2) = -.1092t     divide both sides by -.1092

t = ln(1/2)/-.1092 = about 6.347 days = about 6.3 days (rounded)