2) B = 35 + 335 + 3335 + ... + 3333 .. .. . 35 ⏟
99số3 =
=33 +2 +333+2 +3333+2+...+ 333....33+2
= 2.99 + ( 33+333+3333+...+333...33)
= 198 + 1
3 ( 99+999+9999+...+999...99)
198 + 1
3 ( 10 2 -1 +10 3 - 1+10 4 - 1+ ....+10 100 – 1) = 198 – 33 +
B = ( 10 27 101 − 10 2 ) +165
Bạn đang xem 2) - TAP DE DAP AN THI VAO LOP 10
