問一個數學題ge式

買7鑵可樂under買6鑵送1鑵的優惠:

9.1X6/7

=7.8

買7鑵可樂under normall case:

9.1X7/7

=9.1

so, 9.1-7.8

=1.3

每鑵平$1.3

2007-09-25 17:12:42 補充：
一條式：9.1X7/7-9.1X6/7=$1.3

2007-09-26 12:17:35 補充：
一條式寫晒就係咁樣：(9.1X7)/7-(9.1X6)/7=[ 9.1X (7-6) ] / 7=$1.3 每鑵平$1.3

(7x9.1)/7-(6x9.1)/7
=9.1-7.8
=$1.3

每鑵平
= $ [ 9.1 ( 7-6 )/7 ]
= $ ( 9.1*1/7 )
= $ 1.3