Answer:
0.3
Step-by-step explanation:
0.8/y = 2 : 3/4
The value of y in the above expression can be obtained as follow:
0.8/y = 2 : 3/4
0.8/y = 2 ÷ 3/4
0.8/y = 2 × 4/3
0.8/y = 8/3
Cross multiply
0.8 × 3 = y × 8
2.4 = 8y
Divide both side by the coefficient of y i.e 8
y = 2.4/8
y = 0.3
Thus, the value of y is 0.3
Let the speed of the boat be x
so going against the current the speed is x-7
going with the current the speed is x+7
let the distance be d
time = distance / speed
time to go against the current = d/(x-7)
time to go with the current = d/(x+7)
time going against the current is 3 times going <span>with the current
</span>
d/(x-7) = 3d/(x+7)
⇒⇒⇒ divide by d
1/(x-7)
= 3/(x+7)
x+7
= 3(x-7)
x+7 = 3x - 21
2x = 28
x = 14
So, the speed of the boat in still water is = 14 mph
