數學題 A比C細17歲,B比A細4歲,C比B大二倍,請問他們分別多小歲??

C - A = 17 -----------------------------------------(1)
A - B = 4 ------------------------------------------(2)
C = 2 x B = 2B ----------------------------------(3)

From 2,
A - B = 4
thus, A = 4 + B

From 1,
C - A = 17
2B - 4 - B = 17
B=21

Therefore, A = 4 + 21 = 25

& C = 2 x 21 = 42

A = 25歲
B = 21歲
C = 42歲

a=25歲
b=21歲
c=42歲