1.the maths test is on Monday
2.because their parents are not going to go out at weekends as well
3.they are going to work at home and take care of their children
4.na is going to the library to study instead
 

0,9x50x2+3x51x0,6-0,18x10
=0,9x2x50+3x0,6x51-0,18x10
=0,18x50+0,18x51-0,18x10
=0,18x(50+51-10)
=0,18x91
=16,38

luộc

1+2=3 NO no no
1+2=1x1+2x1
1+2=1x1+(1+1)x1
1+2=1x1+1x1+1x1
1+2=1x(1+1+1)
1+2=1x3
1+2=3

Tuổi con là:
 38-30=8(tuổi)
tuổi mẹ là
38-8=30 tuổi

???

C

=1/2x3+1/3x4+1/4x5+1/5x6
=1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6

=1/2-11/6

=1/3