Answer:
0.36
Step-by-step explanation:
0.4=4/10
0.9=9/10
9/10 times 4/10= (9 times 4)/(10 times 10)=36/100=0.36
Another way you could've done it was to see that since there are 2 decimal points there, the product would also have to have 2 decimal points.
