Three small questions on page 49 of the second volume of the mathematics talent course for the fifth grade of primary school

(50×40×20- 10× 10× 10)÷(50×40)

=(40000- 1000)÷2000

=39000÷2000

=19.5cm

It can also be solved by equations.

Solution: Let the original water depth be x cm.

(50×40×X+ 10× 10× 10 = 50×40×20

2000X+ 1000=40000

2000 x+ 1000- 1000 = 40000- 1000

2000X=39000

2000×2000 = 39000÷2000

X= 19.5

Answer: If this iron block is taken out of the tank, the water level in the tank is19.5cm..