そろばんをはじく

expression, godan verb (-ku)

to count on the abacus; to do abacus calculation

Literal meaning: moving the beads of an abacus to perform arithmetic. The verb はじく (弾く) specifically refers to the flicking motion of the beads.

• 祖そ父ふはそろばんを弾はじくのがとても速はやい。

  My grandfather is very fast at counting on the abacus.

expression, godan verb (-ku)

to calculate cost-benefit; to be guided by self-interest

Figurative extension: to weigh gains and losses, often with a connotation of selfish calculation. Used when someone is thinking only about personal profit or advantage.

• 彼かれはいつもそろばんを弾はじいてから行こう動どうする。

  He always acts after calculating what's in it for him.

• そんなにそろばんを弾はじいてばかりいると、友とも達だちを失うしなうよ。

  If you keep calculating your own benefit like that, you'll lose your friends.