=2/7- 1/7+2/5
= 1/7+2/5
= 19/35
3. 14×2.3+3. 14×3.7
=3. 14×(2.3+3.7)
=3. 14×6
= 18.84
12.5×(6. 1+0.26)×8
=( 12.5×8)×6.36
= 100×6.36
=636
14/ 15× 1/4+ 1/ 15÷4
= 14/ 15× 1/4+ 1/ 15× 1/4
=( 14/ 15+ 1/ 15)× 1/4
= 1× 1/4
= 1/4
930÷[ 1/2×(2/5+4/5)]
=930÷[ 1/2×6/5]
=930÷3/5
= 1550
3 2/5×99+3.4
=3.4×99+3.4
=3.4×(99+ 1)
=3.4× 100
=340