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Ratio & Proportion

Ratio & Proportion. π. Sample Questions & Solutions. Ratio & Proportion. A pitched roof is constructed with a pitch of 1 : 3 rise to span ratio. If the span of the roof is 4.8m, what is its rise 4.8 is = 3 parts so 4.8 ÷ 3 = 1.6 or 1 part 1.6 m = rise

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Ratio & Proportion

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  1. Ratio & Proportion π Sample Questions & Solutions

  2. Ratio & Proportion • A pitched roof is constructed with a pitch of 1 : 3 rise to span ratio. If the span of the roof is 4.8m, what is its rise • 4.8 is = 3 parts so 4.8 ÷ 3 = 1.6 or 1 part • 1.6 m = rise • Or the rise is = 1/3 of the span = 1.6 m rise? 4.8m

  3. Ratio & Proportion • Flat roofs have a fall that does not exceed 1 : 6 ratio of rise to run of falling surface ( 10° pitch approx.) • e.g. A flat roof extends from the rear wall of a house over an extension that is 4.2m further out. Calculate the rise given a ratio of 1 : 9 • 4.2 ÷ 9 = 0.46m • = 460 mm rise Answer

  4. Ratio & Proportion • The recommended fall for 100mm PVC drainage pipe from a domestic dwelling is 1 : 40 • On a run of 7.685m of 100mm waste pipe, by how much will the pipe fall from highest to lowest point assuming a 1 :40 gradient? • 7.685 ÷ 40 = 0.192125 = 192mm Answer

  5. Ratio & Proportion • If the cost of a carpentry project came to a total of €7,850, calculate the cost of each item listed when the ratio is as follows: • Materials cost 2/5 • Labour costs 3/10 • Profit cost 1/10 • VAT cost 1/5

  6. Ratio & Proportion • Firstly, convert all fractions to the same denominator i.e. 2/5 to 4/10 & 1/5 to 2/10 • Now we can divide our total by the denominator (10) so 7,850 ÷ 10 = 785 • Material = 2/5 = 4/10 = 4 x 785 = €3,140 • Labour = 3/10 = 3 x 785 = €2,355 • Profit = 1/10 = 1 x 785 = €785 • VAT = 1/5 = 2/10 = 2 x 785 = €1,570 • 3,140 + 2,355 + 785 + 1,570 = €7,850

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