I f_____ classes at about half past three in the afternoon.(完型填空)一个周长为40cm的长方形,长与宽之比为4:求面积?

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I f_____ classes at about half past three in the afternoon.(完型填空)
一个周长为40cm的长方形,长与宽之比为4:求面积?

设宽为xcm,则长为4xcm
根据已知条件列方程2(4x+x)=40
解得x=4
则长为16,宽为4
面积为“长*宽”即16*4=64cn^2

40÷2=20 20×4/5=16 20×1/5=4 16×4= 64

finished或者原型都行

finish

I finish classes at about half past three in the afternoon.