7 p - 3 u = 30
7 u - 8 p = 30
Find the following values.
- 1 u
- 1 p
(a)
7 p - 3 u = 30 --- (1)
7 u - 8 p = 30 --- (2)
Make p the same.
(1) x 8
56 p - 24 u = 240 --- (3)
(2) x 7
49 u - 56 p = 210 --- (4)
(4) + (3)
49 u - 24 u = 240 + 210
25 u = 450
1 u = 450 ÷ 25 = 18
(b)
Substitute 1 u = 18 into (1).
7 p - 3 u = 30
7 p - 3 x 18 = 30
7 p - 54 = 30
7 p = 30 + 54
7 p = 84
1 p = 84 ÷ 7 = 12
Answer(s): (a) 18; (b) 12