Page 121 - NUMINO_WB_5B

072-P3-1

Decimal Pyramid

What is the 20th digit of the product when 0.3 is multiplied 20 times?
0.3 0.3

0.3 0.3 0.09
0.3 0.3 0.3 0.027
0.3 0.3 0.3 0.3 0.0084
0.3 0.3 0.3 0.3 0.3 0.00243
0.3 0.3 0.3 0.3 0.3 0.3 0.000729

Step 1. When 0.3 is multiplied one time, two times, and three times, how many
decimal places would the products have?

Step 2. When 0.3 is multiplied 20 times, how many decimal places would the
product have?

Step 3. When 0.3 is multiplied continuously, write the last digits of the 10 products
in order.

Step 4. When 0.3 is multiplied 20 times, find the last digit of the product by
finding the pattern of the products’ last digits.