Derivation<\/strong> : <\/h3>\nThe outer surface of a cuboid is made up of six rectangles (rectangular regions, called the faces of the cuboid), whose areas can be found by multiplying length by breadth for each of them seperately and then adding the six areas together.<\/span><\/p>\nNow, if we take the length of cuboid as <\/span>l<\/span>, breadth as <\/span>b <\/span>and the height as <\/span>h<\/span>, then<\/span><\/p>\nThe sum of areas of the six rectangles is:<\/span><\/p>\nArea of rectangle 1 (= <\/span>l <\/span>\u00d7 <\/span>h<\/span>) <\/span>+ Area of rectangle 2 (= <\/span>l <\/span>\u00d7 <\/span>b<\/span>) + Area of rectangle 3 (= <\/span>l <\/span>\u00d7 <\/span>h<\/span>) + Area of rectangle 4 (= <\/span>l <\/span>\u00d7 <\/span>b<\/span>) + Area of rectangle 5 (= <\/span>b <\/span>\u00d7 <\/span>h<\/span>) + Area of rectangle 6 (= <\/span>b <\/span>\u00d7 <\/span>h<\/span>)<\/span><\/p>\n= 2(<\/span>l <\/span>\u00d7 <\/span>b<\/span>) + 2(<\/span>b <\/span>\u00d7 <\/span>h<\/span>) + 2(<\/span>l <\/span>\u00d7 <\/span>h<\/span>)<\/span><\/p>\n= 2(<\/span>lb <\/span>+ <\/span>bh <\/span>+ <\/span>hl<\/span>)<\/span><\/p>\nThis gives us: Total <\/strong><\/span>Surface Area of a Cuboid<\/strong> = 2(<\/span>lb <\/span>+ <\/span>bh <\/span>+ <\/span>hl<\/span>)<\/span><\/p>\nSuppose, out of six faces of a cuboid, we only find the area of four faces, leaving the bottom and top faces. Then in such case, the area of these four faces is called the <\/span>lateral surface area <\/span>of the cuboid. So, <\/span>lateral surface area of a cuboid of length l, breadth b and height h is equal to 2lh + 2bh or 2<\/span>(<\/span>l + b<\/span>)<\/span>h<\/span>.<\/span><\/p>\nThen Lateral Surface Area<\/strong> = 2<\/span>(<\/span>l + b<\/span>)<\/span>h<\/span><\/p>\nExample<\/span><\/strong> : If we have a cuboid whose length, breadth and height are 15 cm, 10 cm and 20 cm respectively, then find its total surface area.<\/span><\/p>\nSolution<\/span><\/strong> : We have l = 15 cm , b = 10 cm and h = 20 cm<\/span><\/p>\nTotal Surface Area = 2[(15 \\(\\times\\) 10) + (10 \\(\\times\\) 20) + (20 \\(\\times\\) 15)] \\(cm^2\\)<\/span><\/p>\nTotal Surface Area = 2(150 + 200 + 300) \\(cm^2\\)<\/span><\/p>\n= 2 \u00d7 650 \\(cm^2\\)<\/span><\/p>\n= 1300 \\(cm^2\\)<\/span><\/p>\n\n\n