7 R + 4 S = 63
8 R + 5 S = 75
Fill in the blanks.
- 1 R = _____
- 1 S = _____
- 5 R + 3 S = _____
(a)
7 R + 4 S = 63 --- (1)
8 R + 5 S = 75 --- (2)
Make S the same.
LCM of 4 and 5 = 20
(1) x 5
35 R + 20 S = 315 --- (3)
(2) x 4
32 R + 20 S = 300 --- (4)
(a)
(3) - (4)
(35 R + 20 S) - (32 R + 20 S) = 315 - 300
35 R - 32 R + 20 S - 20 S = 15
3 R = 15
1 R = 15 ÷ 3 = 5
(b)
Substitute R = 5 into (1).
7 R + 4 S = 63
7 x 5 + 4 S = 63
35 + 4 S = 63
4 S = 63 - 35 = 28
1 S = 28 ÷ 4 = 7
(c)
5 R + 3 S
= 5 x 5 + 3 x 7
= 25 + 21
= 46
Answer(s): (a) 5; (b) 7; (c) 46
