Solution: 9( 1+80%)×80%
=9÷ 1.8×0.8
=4 (hectare)
A: These two kinds of saplings each cover an area of 4 hectares.
Extended data
This topic mainly studies the associative law of multiplication and some relations between common simple multiplication.
The mathematical expression of the law of multiplicative association: a×b×c=a×(b×c).
Commonly used multiplication relations:
( 1)0。 25×4= 1。
(2)25×4= 100。
(3) 1。 25×8= 10。
(4)0。 125×8= 1。
Simple calculation of other required formulas:
(1) subtraction formula 1: a-b-c = a-(b+c).
(2) subtraction formula 2: a-b-c = a-c-b.
(3) The division formula is 1: a ÷ b ÷ c = a ÷ (b× c).
(4) division formula 2: 2:a \b \c = a \c \b b.