MULTIPLICATION IN HEAD


1. Explain how it done!

4 · 60 = 4 · (6 · 10) = (4 · 6) · 10 =24 · 10 = 240
5 · 700 = 5 · (7 · 100) = (5 · 7) · 100 = 35 · 100 = 3 500
2 · 12 000 = (2 · 12) · 1 000 = 24 · 1 000 = 24 000 


How you multiply the zero ending numbers by heart?


2. Compute in head!

6 · 50 = ..........
7 · 30 = ..........
50 · 8 = ..........
40 · 9 = ..........		 4 · 600 = ..........
6 · 900 = ..........
320 · 3 = ..........
180 · 2 = ..........		 7 · 1 200 = ..........
5 · 1 500 = ..........
1 300 · 6 = ..........
1 600 · 4 = ..........


3. Find the numeral value of the letter!

a : 15 = 30
a = ...............
a = ..........		 b : 23 = 40 
b = ...............
b = .......... 		 c : 50 = 16
c = ...............
c = .............

 

4. Find the numeral value of a!

* 10 · a = 10, a = ..........
* 18 · a = 0, a = ..........
* a · a = a, a = .......... 

 5. Compute in head!

370 - 180 + 60 · 5 = ..........
420 + 320 - 80 · 9 = ..........
720 + 250 - 60 · 4 = ..........