Question

假设 $a$ 头奶牛在 $c$ 天里产 $b$ 加仑牛奶。按这个速度， $d$ 头奶牛在 $e$ 天里会产多少加仑牛奶？

Suppose that $a$ cows give $b$ gallons of milk in $c$ days. At this rate, how many gallons of milk will $d$ cows give in $e$ days?

$\dfrac{bde}{ac}$

$\dfrac{ac}{bde}$

$\dfrac{abde}{c}$

$\dfrac{bcde}{a}$

$\dfrac{abc}{de}$

先用 $b$ 乘以 $\dfrac{d}{a}$ ，来调整奶牛数量。

再乘以 $\dfrac{e}{c}$ ，来调整产奶天数。

因此产奶量为 $b \cdot \dfrac{d}{a} \cdot \dfrac{e}{c} = \dfrac{bde}{ac}.$

所以正确答案是 A。

We have to multiply $b$ by $\dfrac{d}{a}$ to account for the new number of cows.

We then have to multiply by $\dfrac{e}{c}$ to account for the new time that we have.

This gives us a final answer of $b \cdot \dfrac{d}{a} \cdot \dfrac{e}{c} = \dfrac{bde}{ac}.$

Thus, A is the correct answer.