You *may find out the box soon if you are lucky. You may think you will have to use the scale ten times if the eleven-gram balls are in the last box. But listen. There is a way to find out the box with eleven-gram balls by 10 using the scale ( ② ). Do you know the way? I'll tell you. First, take a ball or balls out of each box. When you do so, one thing is very important. The *number of the balls and the box number must be the same. For example, you must take one ball out of the No. 1 box, two balls out of the No.2 box, and( 3 )balls out of the No. 10 box. If you do 15 SO, you will have ( 4 ) balls. Next, put all the balls on the scale. Remember all the balls in one box are eleven grams. If the scale shows 553 grams, what does it mean? It means three balls on the scale are eleven grams. オ where (ア balls イ were ウ taken エ these オ カ three ) out of? You kmow the answer, nght? They were in the ( 6 ) 20 box. If the scale shows(7) grams, it means all the balls in the No. 6 box are eleven grams. And if the ( 8 ) box has eleven-gram balls, the scale will show 558 grams. Logical thought is important for you. It is useful to *solve the problem 25 more easily.