Lời giải:

Đổi: 8dm=0,8m

Diện tích quét sơn bằng diện tích xung quanh hình hộp chữ nhật cộng diện tích 1 đáy hình hộp chữ nhật (do không nắp)

Diện tích xung quanh của cái thùng hình hộp chữ nhật không nắp là:

   $(1,5+0,6)\times 2\times 0,8=3,36$ $\left(m^2\right)$

Diện tích đáy là:

   $1,5\times 0,6=0,9$ $\left(m^2\right)$

Diện tích quét sơn là:

   $3,36+0,9=4,26$ $m^2$

                     Đáp số: 4,26 $m^2$

Giải thích:

Diện tích xung quanh của hình hộp chữ nhật là diện tích của một hình hộp chữ nhật mới có chiều dài là $(1,5+0,6)\times 2$, chiều rộng là chiều cao 0,8m.

Diện tích hình chữ nhật = Chiều dài $\times$ Chiều rộng

6,25m3=.6250....dm3

15,3m3=..15300..dm3

0,55m3=..550..dm3

3,952dm3=....3952..cm3

3/4m3=....750000..cm3

25,6m3=..25600000...cm3

=6250dm3

=15300dm3

=550dm3

=3952cm3

=750000cm3

=25600000cm3

Tổng độ dài hai đáy là: 

\(144\times2\div12=24\left(cm\right)\)

Đáy lớn là: 

\(\left(24+6\right)\div2=15\left(cm\right)\)

Đáy bé là: 

\(15-6=9\left(cm\right)\)

tổng 2 đáy là: 144 : 12 x 2 = 24 (cm)

đáy bé là: ( 24 - 6 ) : 2 = 9 (cm)

đáy lớn là: 24 - 9 = 15 (cm)

                            Đ/s...

22,5% của 240 là :

   22,5%x240=54

Hoặc có thể lấy : \(240\times\frac{22,5}{100}=54\)

#H

lấy 240:100x22,5=54

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