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On-line solution of sixth grade math problems
1, the problem of finding the circumference (formula S = ∏ d, ∏-pi, the value is 3. 14.

D-the diameter of the circle is 15 * 2 = 30cm and 20 * 2 = 40cm respectively, so the lengths of the minute hand and the hour hand are 3. 14 * 40 = 125.6cm and 3. 14 * 30 = 90 respectively.

2. Examination of the same knowledge point: the length of two railings is 2 * 3.14 *15 = 94.2m. ..

3. Solution: 1. The flower bed with a diameter of 12m has a total length of 3 * 3.14 *12 =113.04m, and the circumference of a bicycle tire with a diameter of 60cm is 3.1.

Supplementary question: the side length of a square is at least equal to the diameter, which means that the cake can be put down, that is, the area is at least 40*40= 1600 square centimeter, so choose D.