4000-1-2-3-4-5-…-76-77-78=_.
问题描述:
4000-1-2-3-4-5-…-76-77-78=______.
答
4000-1-2-3-4-5-…-76-77-78
=4000-(1+2+3+4+5-…+76+77+78)
=4000-(1+78)×78÷2
=4000-79×78÷2
=4000-3081
=919.
故答案为:919.