Figuring Backwards for the Answers
“What is 48,241 multiplied by 35,482?”
“1,711,687,162,” answered a young man sitting at one end of the stage, before the woman at the other end had time to enter all the digits in a calculator. When the machine finally gave the same answer, the audience applauded.
“569,733 divided by 832?”
“684.77524 with a remainder of 0.00032.” Again the young man got the answer first, using only his fingers, and the calculator confirmed it.
That was in a competition held at the Chinese University of Science and Technology in May 1978, and the mathematical genius was 24-year-old Shi Fengshou from Shaanxi Province, China. “On question after question put by the audience,” reports “China Reconstructs,” “the man won.”
Shi Fengshou developed his astounding technique strictly through hard work and inventive thinking. While still in the village primary school, he often wondered why people would read a number from left to right but do calculations from right to left. Wouldn’t it be much simpler if everything were done the same way? This started him on the search for a fast way of doing mental calculations.
Working from left to right enabled Shi to give out the answer as soon as each digit was obtained, a definite advantage in mental computations. But the key to his success was in his ingenious way of handling the carry-over. For example, try multiplying 36 by 2 from the left, mentally. The first digit of the answer is not 6 (2 × 3) but 7 because there is a carry-over of 1 from the next operation (2 × 6 = 12). So the answer is 72. From this simple idea, Shi determined that every time a digit is multiplied by 2, the product should be increased by 1 if the next digit is 5 or greater. From there, he worked out the rules for the numbers 3 through 9, and soon such calculations became simple child’s play for him. By the time he graduated from primary school, he had already mastered calculations involving multidigit numbers, such as those he did in the competition.
Later, Shi also developed methods for doing powers and roots and even logarithmic and trigonometric functions mentally. The story had it that he would practice squaring license-plate numbers, that is, multiplying the number by itself. License numbers in China are seven digits long. Can you imagine standing on the street trying to square a seven-digit number? At first, the car would be long gone before he could come up with the answer. But, with practice, he would have it as soon as the car had passed.
It was not long before he attracted professional attention. Eventually his work was published in a book entitled “Quick Calculations,” which became very popular all through China.
Minds like Shi’s are rare, but they demonstrate the immense potential of the human brain. Granted that not all of us are interested in becoming a “human calculator” like Shi Fengshou, but imagine the things that we can learn to do and enjoy when given unlimited time—an eternity—a prospect that the Bible holds out to lovers of the true God.
[Picture on page 11]
Shi Fengshou explains how he does it