Mike and bill sell cars for jangles auto. over the past year they sold 640 cars. assuming mike sells 3 times as amny as bill, how many cars did mke sell?

Let Mike sold M cars and Bill sold B cars. 
Now both sold 640 cars in total, means M + B = 640, 
also Mike sold 3 times as many as Bill, means M = 3*B. So our equations became, 
M + B = 640, & M = 3*B, put value of M in terms of B. 
3*B + B = 640, 4*B = 640, 
B = 640/4, B = 160, as M = 3*B, M = 3*160 = 480. 
So Mike sold 480 cars & Bill sold 160 cars.

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