Anonymous
Anonymous asked in Education & ReferenceHomework Help · 3 weeks ago

help me with math homework please ?

a boat can go 12 km along the water current in 2 hours. the return trip takes 3 hours against the water current. what is the speed of the boat in still water and the speed of the water current?

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  • RR
    Lv 7
    3 weeks ago

    Downstream: 12km in 2 hours = 12/2 =  6kph

    Upstream: 12 km in 3 hours = 12/3 = 4 kph

    Average speed = (6 + 4)/2 = 5 kph

    The speed of the boat in still water is 5 kph

    6 - 5 = 1

    or

    5 - 4 = 1

    The current is 1 kph

    ANS Boat = 5 kph. Current is 1 kph

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  • 3 weeks ago

    Let the boat's speed in still water = b and the river's speed = r

    (b+r)*2 = 12km

    2b+2r= 12km

    (b-r)*3 = 12km

    3b-3r = 12km Multiply equation by 2/3

    2b-2r = 8  Subtract from 2b+2r = 12

    4r = 4 so r = 1km/hr = current speed.  

    Substitute into 2b+2r=12

    2b+2 = 12

    2b = 10, b = 5km/hr = boat's speed in still water

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  • Alan
    Lv 7
    3 weeks ago

    let r= speed in still water km/hr 

    let c = rate of current km/hr

    (r +c)2  = 12  

    (r-c) 3  =12 

    2r +2c  =12 

    3r-3c =12       

    multiply 1st by 3 and 2nd by 2 

    6r + 6c  = 36 

    6r - 6c   = 24  

    now add the 2 equation 

    12r  = 60 

    r  = 60/12 =5 km/hr

    speed in still water= 5 km/hr

    2*5 + 2c = 12  

    10 + 2c =12 

    2c  = 12 -10 

    2c =2 

    c = 2/2 =1 km/hr

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