\(1 cm^2 = 1 cm\)

\(1km^2 = 100000000dm^2\)

nửa chu vi là

\(270:2=135(cm)\)

chiều dài là

\((135+15):2=75(cm)\)

chiều rộng là

\(135-75=60(cm)\)

DT là

\(75x60= 4500(cm^2)\)

\(42 = 2.3.7 \)

\(72=2^3.3^2\)

\(180=2^2.3^2.5\)

\(=>BCNN(42,72,180)=\)\(2^3.3^2.5.7=2520\)

\(x+2=3\)

\(x=3-2\)

\(x=1\)

\(----------\)

\(x+23=50\)

\(x=50-23\)

\(x=27\)

\(---------\)\(--\)

\(33+x=45\)

\(x=45-33\)

\(x=12\)

\(------------\)

\(15+x=70\)

\(x=70-15\)

\(x= 55\)

\(--------------\)

\(61+x=100\)

\(x=100-61\)

\(x= 39\)

\(--------------\)

\(x-5=23\)

\(x=23+5\)

\(x=28\)

\(-------------\)

\(x-23=98\)

\(x=98+23\)

\(x= 121\)

\(-------------\)

\(435-x=125\)

\(x=435-125\)

\(x= 310\)

\(------------------\)

\(321-x=50\)

\(x=321-50\)

\(x= 271\)

\(----------------\)

\(x.9=108\)

\(x=108:9\)

\(x= 12\)

\(-------------\)

\(x.23=184\)

\(x=184:23\)

\(x= 8\)

\(-----------\)\(---\)

\(5.x=35\)

\(x=35:5\)

\(x=7\)

\(------------------\)

\(x:3=9\)

\(x=9.3\)

\(x=27\)

dừa 

\(\dfrac{\text{60 }}{11}:15=\dfrac{\text{60 }}{11}\)\(\text{ x}\dfrac{\text{1}}{5}=\)\(\dfrac{4}{11}\)

\(8\) phút \(54\) giây \(:2=\)\(4\) phút \(27\) giây