8/17×7/10+7/10×9/17+3/10
=(8/17+9/17)×7/10+3/10
=1×7/10+3/10
=7/10+3/10
=1
0.84÷【7/10×（1/2×7/2）】
=0.84÷【7/10×7/4】
=84/100÷49/40
=21/25×10/49
=3/5×2/7
=6/35