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Tìm x, biết:
a) y + 30%y = -1, 3 b) \(y – 25\% y = {1 \over 2}\)
c) \(3{1 \over 3}y + 16{3 \over 4} = – 13,25\)
Giải
a) y + 30%y = -1, 3
(1+30%) y = -1, 3
\(\eqalign{
& {{130} \over {100}}y = – 1,3 \cr
& y = {{ – 13} \over {10}}:{{130} \over {100}} \cr
& y = {{ – 13} \over {10}}.{{100} \over {130}} = – 1 \cr} \)
b) \(y – 25\% y = {1 \over 2}\)
\(\left( {1 – 25\% } \right)y = {1 \over 2}\)
\(\eqalign{
& {{75} \over {100}}y = {1 \over 2} \cr
& y = {1 \over 2}:{{75} \over {100}} \cr
& y = {1 \over 2}.{{100} \over {75}} = {2 \over 3} \cr} \)
c) \(3{1 \over 3}y + 16{3 \over 4} = – 13,25\)
\(\eqalign{
& {{10} \over 3}y = – 13{1 \over 4} – 16{3 \over 4} \cr
& {{10} \over 3}y = – 30 \cr
& y = – 30:{{10} \over 3} = – 30.{3 \over {10}} = – 9 \cr} \)