Stephanie M. answered 07/20/15
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Let x = number of mountain bikes and let y = number of racing bikes.
The amount of time it will take to put all the bikes together must equal 390 hours. So:
2x + 2.5y = 390
The amount of money it will take to buy all the bikes must equal $63,000. So:
300x + 420y = 63000
Now you have a system of equations:
2x + 2.5y = 390
300x + 420y = 63000
Solve the first equation for x, then plug that into the second equation and solve for y:
2x = 390 - 2.5y
x = 195 - 1.25y
300x + 420y = 63000
300(195 - 1.25y) + 420y = 63000
58500 - 375y + 420y = 63000
58500 + 45y = 63000
45y = 4500
y = 100
Now, plug that value into the first equation to solve for x:
2x + 2.5(100) = 390
2x + 250 = 390
2x = 140
x = 70
The shop can buy and assemble x = 70 mountain bikes and y = 100 racing bikes.