I am sure you have all seen riddles like:

3 men eat out, the bill is R300, they split it R100 each + pay cash. The waiter comes back and says the meal only comes to R250, so gives each a R10 back and keeps R20 as a tip. So each man pays R90.

R90 x 3 = R270 and R270 + R20 = R290. Where did the other R10 go?

There is a good explanation on http://www.answerbag.com/q_view/103886

The mathematics can confuse you if you add numbers that are not supposed to be added or work out percentages on the incorrect amounts:

In activity 6 of Module 1_3 the user is asked to type in the final amount the group at a restaurant is willing to spend on (foodAndDrink + TIP + VAT) and the program is supposed to calculate what the foodAndDrink without the VAT and TIP should be. We normally calculate the VAT on foodAndDrink and the 10% TIP on the bill that includes VAT and foodAndDrink

foodAndDrink + 14%* foodAndDrink + 10%* (food and drink+ 14%* foodAndDrink ) = totalBill

foodAndDrink + 14%* foodAndDrink + 10%* (food and drink+ 14%* foodAndDrink ) = totalBill

foodAndDrink + VAT + TIP = totalBill

SAY foodAndDrink = X

X + 0.14*X + 0.1*(X*1.14) = totalBill

X + 0.14*X + 0.114*X = totalBill

X(0.114+0.14+1) = totalbill

X(1.254) = totalBill

Therefore X = totalBill/(1.254)

If you say the tip = totalBill/1.1 you are working with 10% of the totalbill

instead of 10% of the foodAndDrink and VAT and the ratio will give incorrect answers and similarly the VAT is not equal to totalBill/1.14

The scratch solution can also look like this:

The scratch solution can also look like this:

when green flag clicked

ask "What should your final bill be?" and wait

set "

**FinalBill**" to (answer) set "

**AfterTip**" to ((**FinalBill**) / 1.1) set "

**AfterVAT**" to ((**AfterTip**) / 1.14) say (join "R " (

**AfterVAT**)) for 2 secs. (LilanĂ© le Grange, Fourways High School)
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