Problem from an Indian math textbook

A correct answer explained by mathematician.
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[@subasu478]

40 or 80/2

[@anacristinavazquezhernande8998]

40

[@manuelquitevis6794]

30 + 10 = 40 ( c) 80/2= 40

[@rgrinnell]

C 40

[@JoanBalser]

C

[@mariajimenez2706]

20

[@mariajimenez2706]

80/2

[@lucilialobo6773]

Dá 80/2

[@Dubravka-pe6ul]

30+30=60÷3=20

[@joepkortekaas8813]

Learn simple calculating!

[@ShivShankarSharma-j8w]

40

[@michellestreiff-wilmot7523]

C

[@vijayalakshmivenkataraman3517]

20

[@ljupkaivanovska1275]

40