mary and susan have 100 postcard in total.on susan's birthday,mary gives four over five of her postcard to susan.if susan has 85 postcards now.find the original number of postcards that mary has

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mary and susan have 100 postcard in total.on susan's birthday,mary gives four over five of her postcard to susan.if susan has 85 postcards now.find the original number of postcards that mary has
mary and susan have 100 postcard in total.on susan's birthday,mary gives four over five of her postcard to susan.if susan has 85 postcards now.find the original number of postcards that mary has

mary and susan have 100 postcard in total.on susan's birthday,mary gives four over five of her postcard to susan.if susan has 85 postcards now.find the original number of postcards that mary has
【参考答案】

susan现在有卡85张,则mary现在有卡100-85=15张.
设mary原有卡m张,susan原有卡100-m张
(100-m)+[(4/5)m]=85
100-m+(4/5)m=85
100-(1/5)m=85
(1/5)m=15
m=75
于是,mary原来的卡片是75张.

mary 有 a个card susan有b个card
a+b=100
4/5 a + b = 85
求a，有1/5 a = 15 => a=75
因此marry有75张卡。
望采纳，谢谢！

连接AC、BD交于O，连OE。由正方形ABCD有AC垂直BD于O，又PD垂直底面ABCD，所以PD垂直AC，故AC垂直平面PDB于O，即希望对你能有所帮助。...

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连接AC、BD交于O，连OE。由正方形ABCD有AC垂直BD于O，又PD垂直底面ABCD，所以PD垂直AC，故AC垂直平面PDB于O，即希望对你能有所帮助。

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