2. This is actually the problem of finding the common multiple. First, according to the calculation of 300 meters by 5 meters, 60 pits are needed.
However, 30 pits have been dug before, and it depends on whether it can be dug like a 5-meter pit. The least common multiple of No.3 pit and No.5 pit is 15 90/ 15=6, which means that the six pits dug before can still be used if dug again, so the answer is 60-6=54.
3. A cycle has15 *14/2 =105 combinations.
That is 105 8 hours.
105*8/3=35 days
4.A =4/ 13,5/6 A = B,4/ 1 1 (A+B) = C,D-C =4000。
The substitution method gives 156000. If there is an option, you don't need to calculate it carefully, just eliminate the interference term.
A.18.6 million B.15.6 million C.210.8 million D.22.3 million
[answer] b
[Resolution] The population of Area A is the population of the whole city (4/ 13), so the population of the whole city is a multiple of 13. Combination options, select B.
5. The answer is 15. This is a variation of a product sequence. Law: (item 1-3) × (item 2-3) = item 3.