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Question

In a mathematics class, 20 children had forgotten their rulers and 17 forgotten their pencils. "Go and borrow them from someone at once”, said the teacher. If 24 children left the room, then the number of children who had forgotten both is ____. 


  1. 11

  2. 12

  3. 13

  4. 14


Solution

The correct option is C

13


Let the R be the set of children forgotten Ruler, P be the set of children forgotten Pencil.

Given that,

n(R)=20,n(P)=17

n(RP)=24

n(RP)=n(R)+n(P)n(RP)

n(RP)=20+1724=13

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