请教机警一道！

bigmouse

1. 共78个大人参加一个带小孩去的野炊之类的活动，其中35个自愿照看小孩，有11个自愿又照顾小孩又带吃的，现在告诉已知自愿带吃的大人的数量是既不照看小孩，又不带吃的大人的数量的1。5倍，问带吃的大人有多少？
【确定】36
请教解题思路！

lisaislisa

I wonder sth wrong with the number available
anyway , the way to deal with the problem is like the following
P(A)=ppl who willing to take care of the kids =35
P(B)=ppl who willing to take food=x
P(A and B)=ppl who willing to take care of the kids and to take food=11
P(A or B ) =ppl who either willing to take care of the kids or to take food
P(I)=number of the ppl=78
P(notA,notB)=ppl who neither willing to take care of the  kids nor to take food
=78-P(AorB)=x/1.5=>(AorB)=(117-x)/1.5
P(AorB)=P(A)+P(B)-P(AandB)=>x=81/2.5
if the answer is 36
ppl who willing to take food will be twice as many as those who neither willing to take care of kids nor take food , but not 1.5 times

anyway , as victor saids , idea is the most important
^^