Let a1,a2,a3,…a4001 are in A.P. such that 1a1a2+1a2a3+….+1a4000a4001=10 and a2+a4000=50 then a1−a4001 is equal to

4000a1a4001=10⇒a1a4001=400 also a1+a4001=50⇒a1−a40012=a1+a40012-4a1a4001                                                   =2500-1600                                                   =900⇒a1−a4001=30