F.1 Maths ( easy)

A bookshop sold all the books at 20% discount in a summer sale. If a costumer paid with a credit card, he or she needed to pay an extra service charge of 3%. Eric bought 8 books and the total marked price was $425.
How much did he pay if he use a credit card?
你可以先計這這書折扣後的價錢：
425 x (1 – 20%) = 340元
再加 3% 的信用卡收費：
340 x (1 + 3%) = 350.2元
所以他用信用卡要付 350.2元

你可以先計這這書折扣後的價錢: Selling price of the book after the discount.

425 - ( 425 x 20%) = 425 x (1 – 20%)
= 425 x 80%
= ($340)

加 3% 的信用卡收費：Selling price of the book after add an extra service charge of 3%

340 + (340 x 3%) = 340 x ( 1+3%)
= 340 x 103%
= ($350.2)

所以他用信用卡要付 350.2元 He paid $350.2 if he used a credit card.

成條式就係咁..

425 x ( 1-20%) x (1+3%)
= 425 x 80% x 103%
= ($350.2)

He paid $350.2 if he used a credit card.

好容易!
Eric用credit card被錢要被多3%
咁我地先計下d book discount完幾錢:
$425(1-0.2or20%)= $340
之後計佢用cedit card要幾錢啦:
$340(1+0.03or3%)= $350.2

成條式係
$425(1-20%)(1+3%)=$425(80%)(103%)= $350.2

Eric need to pay if he use a credit card
=$425 x (1 - 20%) x (1 + 3%)
=$350.2

首先$425 x (1 - 20%)是要計出selling price
(1 + 3%)是加上了 extra service charge 。
很易計

$425x(1-20%) 就等於discount後既selling price,
咁就會計到個selling price系$340.
$340x(1+3%)就會係加埋extra service charge 個3%之後既price
所以成條式就系:
425x(1-20%)x(1+3%)!!
答案應該計到系$350.2~