She could read the mental calculations he was making as they took place.

In the end, there was no time to finish the mental calculation.

The older man took in his situation and did some rapid mental calculations.

He closed his eyes for a moment, and made some mental calculations.

Together, they did a quick mental calculation and she agreed with him about the price.

Ten more days, she noted after a quick mental calculation.

He has held world records for mental calculation in the past.

He stopped his mental calculations and looked up at her.

With less than 45 minutes until the meeting, you do a quick mental calculation.

Martha thought for a moment, making mental calculations, trying to remember what happened on which day.