13) 
64  x 4 + 18 x 4 + 9 x 8
= 64 x 4 + 18 x 4 + 18 x4
= 4 × ( 64+18+18)
= 4 × 100
= 400
14) 
44 x 5 + 18 x 10 + 20 x 5
= 44 × 5 + 36 × 5 + 20 × 5
= 5 × (44 + 36 + 20)
= 5 × 100
= 500
 

13/
64  x 4 + 18 x 4 + 9 x 8 = 64 x 4 + 18 x 4 + 18 x 4 = 4 × ( 64+18+18) = 4 × 100 = 400
14/ 
44 x 5 + 18 x 10 + 20 x 5 = 44 × 5 + 36 × 5 + 20 × 5 = 5 × (44 + 36 + 20) = 5 × 100 = 500
15/
3 x 4 + 4 x 6 + 9 x 2 + 18 = 4 x (3 + 6) + 18 + 18 = 4 x 18 + 18 + 18 = 18 x 4 = 72
Hok tốt
 

64 x 4 + 18 x 4 + 9 x 8
= 64 x4 + 18 x 4 + 18 x 4
= 4 x ( 64 + 18 +18 )
= 4 x 100
= 400