Kneel for parallel education, mathematical thinking guidance, sixth grade, volume 2, score first, answer quickly! Will be supplemented! ! Will add pages and topics [there are three questions below.

(78.6-0.786×25+75%×2 1.4)÷ 15× 1997

=[ 78.6-0.786×25+75%×( 100-78.6)]÷ 15× 1997

= (78.6-78.6%×25+75%× 100-75%×78.6)÷ 15× 1997

=﹙ 78.6- 78.6%×25 + 75- 75%×78.6﹚÷ 15× 1997

=﹙ 78.6- 78.6%×25 + 75- 75×78.6%﹚÷ 15× 1997

= [78.6- 78.6%×﹙25 + 75﹚﹢75]÷ 15× 1997

=75÷ 15× 1997

=5× 1997

=9985

﹙ 1+ 1/2+ 1/3+ 1/4﹚×﹙ 1/2+ 1/3+ 1/4+ 1/5﹚-﹙ 1+ 1/2+ 1/3+ 1/4+ 1/5﹚×﹙ 1/2+ 1/3+ 1/4﹚

=﹙ 1+ 1/2+ 1/3+ 1/4+ 1/5- 1/5﹚×﹙ 1/2+ 1/3+ 1/4+ 1/5﹚-﹙ 1+ 1/2+ / kloc-0//3+ 1/4+ 1/5﹚×﹙ 1/2+ 1/3+ 1/4﹚

=﹙ 1+ 1/2+ 1/3+ 1/4+ 1/5﹚×﹙ 1/2+ 1/3+ 1/4+ 1/5﹚- 1/5×﹙ 1/2+ 1/3+ / kloc-0//4+ 1/5﹚-﹙65438 +0+ 1/2+ 1/3+ 1/4+ 1/5﹚×﹙ 1/2+ 1/3+ 1/4﹚

=﹙ 1+ 1/2+ 1/3+ 1/4+ 1/5﹚× [﹙ 1/2+ 1/3+ 1/4+ 1/5﹚-﹙ 1/2+ 1/3+ 1/4﹚

]- 1/5×﹙ 1/2+ 1/3+ 1/4+ 1/5﹚

=﹙ 1+ 1/2+ 1/3+ 1/4+ 1/5﹚× 1/5 - 1/5×﹙ 1/2+ 1/3+ 1/4+ 1/5﹚

= 1/5

I didn't see the topic clearly.

Same idea as above.

﹙ 1+0.23+0.34﹚×﹙0.23+0.34+0.65﹚-﹙ 1+0.23+0.34+0.65﹚×﹙0.23+0.34﹚

=﹙ 1+0.23+0.34 + 0.65 -0.65﹚×﹙0.23+0.34+0.65﹚-﹙ 1+0.23+0.34+0.65﹚×﹙0.23+0.34﹚

=﹙ 1+0.23+0.34 + 0.65 ﹚×﹙0.23+0.34+0.65﹚-0.65×﹙0.23+0.34+0.65﹚-﹙ 1+0.23+0.34+0.65﹚×﹙0.23+0.34﹚

=﹙ 1+0.23+0.34 + 0.65 ﹚×[﹙0.23+0.34+0.65﹚-﹙0.23+0.34﹚]-0.65×﹙0.23+0.34+0.65﹚

=﹙ 1+0.23+0.34 + 0.65 ﹚×0.65-0.65×﹙0.23+0.34+0.65﹚

= 1×0.65 +﹙0.23+0.34+0.65﹚×0.65-0.65×﹙0.23+0.34+0.65﹚

=0.65

Do more questions and sum up experience. It is not difficult