Answer:
a)(11-7)+3
=(4)+3
=7
b)4.3+10.2
=12+20
=32
c)35÷7.4-15.8
=5.4-15.8
=20-120
=-100
I don't know about the first one but for the second one:
First you have all ten books, but then every time after, you loose one because you can't put the same book in the group twice.
10 * 9 * 8 * 7 = 5040 groups
