Which number equals 9 cross times 100 plus 9 cross times 10 plus 0 cross times 1 plus 0 cross times 1 over 10 plus 3 cross times 1 over 100 plus 7 cross times fraction numerator 1 over denominator 1 comma 000 end fraction ?

Step-by-step explanation:

(9x100)+(9x10)+(0x1)

Let the current speed be "c";

Then the boat speed in still wate is "5c":

Upstream speed:

distance = 12 miles ; rate = 5c-c = 4c mph ; time = 12/4c = 3/c hrs

Downstream speed:

distance = 12 miles ; rate = 5c+c = 6c mph ; time = 12/6c = 2/c hrs

Step-by-step explanation:

Equation:

time + time = 2 1/2 hrs

3/c + 2/c = 5/2

Multiply thru by 2c to get:

6 + 4 = 5c

c = 2 mph (speed of the current)

5c = 10 mph (speed of the boat in still water)