1÷( 1/3÷5)
= 1÷ 1/ 15
= 15 (days)
A building is 70 meters long, 50 meters wide and 80 meters high. In order to add festive atmosphere, Uncle Zhang went to the store to buy colored lights to decorate the building. How many bundles of colored lights should he buy? Each bundle 100 meter
(70×2+50×2+80×4)÷ 100
=560÷ 100
=5.6 is approximately equal to 6 (beam)
3. A rectangular piece of iron sheet, 40 cm long and 30 cm wide, was cut out from the periphery to make a box with a side length of 6 cm. What is the surface area and volume of this box?
Surface area: 40×30-6×6×4= 1056 (square centimeter)
Volume: (40-6×2)×(30-6×2)×6
=28× 18×6
=3024 (cubic centimeter)
4. Forge an 8 cm long billet into a rectangular steel plate with a length of 16 cm and a width of 5 cm. How thick is this steel plate?
8×8×8÷( 16×5)
=5 12÷80
=6.4 cm