问一道题：NO.PZ2017100901000005 [ CFA I ]

NO.PZ2017100901000005 问题如下 invial’s manfor onions is given the following equation:Qo=3−0.05P0​+0.009I−0.16Pt​where Qo is the number of onions man P0​ is the priper pounof onions, I is the householincome, anPt​ is the priper pounof tomatoes. If the priof onions is $1.25, householincome is $2,500, anthe priof tomatoes is $3.75, the cross-prielasticity of manfor onions with respeto the priof tomatoes is closest to: A.–1.0597. B.–0.0242. C.–0.0081 B is correct.The cross-prielasticity of manmeasures the responsiveness of the manfor onions in response to a change in the priof tomatoes. From the manfunction equation:Qo=3−0.05P0​+0.009I−0.16Pt​Qo=3-0.05( 1.25 ) +0.009( 2,500 )-0.16( 3.75 ) = 24.8375a priof onions of $1.25 ana priof tomatoes of $3.75, the cross-prielasticity of manis calculatefollows: Cross-prielasticity of man= (ΔQo /ΔPt ) × ( P t / Qo ) Cross-prielasticity of man= –0.16 × (3.75/24.8375) = –0.0242考点交叉价格弹性解析把题目中给定的各项数据带入需求函数公式中，求解需求量。即Qo=3−0.05P0​+0.009I−0.16Pt​Qo=3-0.05( 1.25 ) +0.009( 2,500 )-0.16( 3.75 ) = 24.8375接着利用需求交叉弹性公式计算结果，即( (ΔQo /ΔPt ) × ( P t / Qo ) Cross-prielasticity of man= –0.16 × (3.75/24.8375) = –0.0242 請問ΔQo/ΔPt爲何等於-0.16？Qo=3-0.05( 1.25 ) +0.009( 2,500 )-0.16( 3.75 ) = 24.8375Qo不是應該24.8375嗎？那結果不應該是ΔQo/ΔPt=24.8375/3.75（土豆價格）=6.623 ？？能説下ΔQo與ΔPt的具體計算步驟嗎？謝謝

NO.PZ2017100901000005 –0.0242. –0.0081 B is correct. The cross-prielasticity of manmeasures the responsiveness of the manfor onions in response to a change in the priof tomatoes. From the manfunction equation: Qo=3−0.05P0​+0.009I−0.16Pt​ Qo=3-0.05( 1.25 ) +0.009( 2,500 )-0.16( 3.75 ) = 24.8375 a priof onions of $1.25 ana priof tomatoes of $3.75, the cross-prielasticity of manis calculatefollows: Cross-prielasticity of man= (ΔQo/ΔPt ) × ( P t / Qo) Cross-prielasticity of man= –0.16 × (3.75/24.8375) = –0.0242 考点交叉价格弹性 解析 把题目中给定的各项数据带入需求函数公式中，求解需求量。即 Qo=3−0.05P0​+0.009I−0.16Pt​ Qo=3-0.05( 1.25 ) +0.009( 2,500 )-0.16( 3.75 ) = 24.8375 接着利用需求交叉弹性公式计算结果，即( (ΔQo/ΔPt ) × ( P t / Qo) Cross-prielasticity of man= –0.16 × (3.75/24.8375) = –0.0242老师你好，请问题干给出的onion洋葱和tomatoes西红柿应该是替代品吧？那么它们的交叉弹性e应该是大于零，为正数吧？

–0.0242. –0.0081 B is correct. The cross-prielasticity of manmeasures the responsiveness of the manfor onions in response to a change in the priof tomatoes. From the manfunction equation: Qo=3−0.05P0​+0.009I−0.16Pt​ Qo=3-0.05( 1.25 ) +0.009( 2,500 )-0.16( 3.75 ) = 24.8375 a priof onions of $1.25 ana priof tomatoes of $3.75, the cross-prielasticity of manis calculatefollows: Cross-prielasticity of man= (ΔQo/ΔPt ) × ( P t / Qo) Cross-prielasticity of man= –0.16 × (3.75/24.8375) = –0.0242 考点交叉价格弹性 解析 把题目中给定的各项数据带入需求函数公式中，求解需求量。即 Qo=3−0.05P0​+0.009I−0.16Pt​ Qo=3-0.05( 1.25 ) +0.009( 2,500 )-0.16( 3.75 ) = 24.8375 接着利用需求交叉弹性公式计算结果，即( (ΔQo/ΔPt ) × ( P t / Qo) Cross-prielasticity of man= –0.16 × (3.75/24.8375) = –0.0242为什么前半部分等于0.16？