The question might have been solved without reducing 17s. 4d. to pence, thus:
- yds. yds. s. d.
- 22 : 156 ∷ 17 . 4
- 156(227)
- 22) £135 . 4 . 0(£6 . 2 . 10¾-⁷/₁₁ (228)
- 132
- 3 × 20 + 4 = 64
- 44
- 20 × 12 = 240
- 220
- 20 × 4 = 80
- 66
- 14
The student must learn by practice which is the most convenient method for any particular case, as no rule can be given.
241. It may happen that the three given quantities are all of one denomination; nevertheless it will be found that two of them are of one, and the third of another sort. For example: What must an income of £400 pay towards an income-tax of 4s. 6d. in the pound? Here the three given quantities are, £400, 4s. 6d., and £1, which are all of the same species, viz. money. Nevertheless, the first and third are income; the second is a tax, and the answer is also a tax; and therefore, by (152), the quantities must be placed thus:
£1 : £400 ∷ 4s. 6d.
242. The following exercises either depend directly upon this rule, or can be shewn to do so by a little consideration. There are many questions of the sort, which will require some exercise of ingenuity before the method of applying the rule can be found.
EXERCISES.
If 15 cwt. 2 qrs. cost £198. 15. 4, what does 1 qr. 22 lbs. cost?
Answer, £5 . 14 . 5 ¾ ¹⁸⁵/₂₁₇.
If a horse go 14 m. 3 fur. 27 yds. in 3ʰ 26ᵐ 12ˢ, how long will he be in going 23 miles?