\(< =>42-x-1\cdot3=9< =>42-x-3=9< =>42-x=12< =>x=10\)

10/3

b,c quen mat

C

= (3268-268)+(1743+257)

= 3000 + 2000

= 5000

ghi lon

= (3268-268)+(1734+257)

= 3000+1991

=4991

\(=\dfrac{5}{7}.\dfrac{2}{1}\)

\(=\dfrac{10}{7}\)

tu da

5+1+1+1+1+1+1

= 12

\(=\dfrac{1}{2}.10+\dfrac{1}{3}.3+\dfrac{1}{4}.4+\dfrac{1}{5}.5+\dfrac{1}{6}.6+\dfrac{1}{7}.7+\dfrac{1}{8}.8+\dfrac{1}{9}.9 \)

\(=5.1.1.1.1.1.1.1\)

= 5