Question 795281
Volume of pyramid = length * width of base * height *1/3
Volume of pyramid = 10 * 10 * 27 * 1/3 = 900 cm^3
Volume of tank required to just cover pyramid
 = length * width of base * height (pyramid)
= 60 * 20 * 27 = 32400 cm^3
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the pyramid is now removed;
32400 - 900 = 31500 cm^3
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New height of liquid:-
31500 cm^3 = 60 * 20 * height
height = 31500/(60 * 20)= 26.25 cm

A fall of 0.75 cm.
Hope this helps.
;-)