Main questions by teacher and anticipated students' responses 
Remarks on teaching 
 Let's calculate 18 x 25 using your calculator.
 Without using key "5", how do you calculate 18 x 25 on your
calculator?

 Make sure every student calculates 18 x 25 with a calculator.
 Let students understand that they can use any other keys including
"+", "", "÷".

 Let students solve the problem individually.

 If students need help, give them the work sheet.

 Compare students' solution and find the ideas behind their solutions.
 18+18+18+18+18+18+18+18+18+ 18+18+18+18+18+18+18+18+18+ 18+18+18+18+18+18+18=450
 18 x 24 +18=450
 18 x26 18=450
 18 x19 + 18 x 6=450
 18 x100 ÷4=450
There should be many other answers.

 Ask the students who present their solution for other students to explain
how to find the way to get the answer without using key "5",
in order to help all other students understand the idea behind the solutions.

 Summing up by teacher.
 Teacher sums up all the ideas that students use to calculate 18 x 25
without using key "5".
 Exercise
 Calculate 18 x 25 without using key "2".

Let each student write short journal about what he / she learned through
this lesson. 