F.1數學3條ratio 急~~ 15點

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1b)Given 3a=2c , b is twice of a , where a ,b and c are non-zero,find
a:b:c.
3a = 2c, a:c = 2:3,
b = 2a, b:a = 2:1, b:a = 4:2
Hence, a:b:c = 2:4:3
2) Sammy got 220 marks in three Mathematics tests.The ratio of his score
in the first test to that in the second test is 8:9 , while the ratio
of his score in the second test to that in the third test is 6:7.Find
Sammy's score in each test.
R_1 : R_2 = 8:9 = 16:18
R_2 : R_3 = 6:7 = 18:21
R_1:R_2:R_3 = 16:18:21
Sammy's score in 1st test
= 16/(16+18+21) * 220
= 64
The score in 2nd test
= 18/(16+18+21) * 220
= 72
The score in 3rd test
= 220 - 64 - 72
= 84
3)the lengths of 3 wires are in the ratio of 13:15:12 . If the shortest
wire is 180 cm long,find the total length of the 3 wires.

Total length of the 3 wires
= 180/[12/(13+15+12)]
= 15(40)
= 600 cm