Đáp án:
a)Ta có:5A+5B+5C=12 P
5B+5C+5D=15 P
5A+5D=30 P
=>(5A+5B+5C+5D)x2=12 P+15 P+30 P
(5A+5B+5C+5D)x2=57 P
5A+5B+5C+5D=28 P 30 Giây
b)
Ta có:5A+5B+5C=12 P
5B+5C+5D=15 P
5A+5D=30 P
=>(5A+5B+5C+5D)x2=12 P+15 P+30 P
(5A+5B+5C+5D)x2=57 P
5A+5B+5C+5D=28 P 30 Giây
5A=28 P 30 Giây-15 P
5A=13 P