( 1) 18+8×9

= 18+72

=90 (yuan)

(2)20-9×2

=20- 18

=2 (yuan)

(3) 18×2+8×3

=36+24

=60 (yuan)

definition

Addition: the operation of combining two numbers into one number.

Subtraction: when two addends and one of them are known, the operation of finding the other addend.

Multiplication: the operation of finding the product of two numbers.

Division: the operation of finding another factor by knowing the product of two factors and one of them.