(-3.85)x(-13)+(-13)x(-6.15)+0.79x7/15+8/15x0.79
=(-13)(-3.85-6.15)+0.79x(7/15+8/15)
=130+0.79
=130.79
999+24/25x(-5)
=999+（1-1/25）×（-5）
=999-5+1/25×5
=999-5+1/5
=994又1/5