问题 解答题

布袋中有38个同样大小的小球,其中白、黄、红三种颜色的球各有10个,另外还有3个蓝球、3个绿球和2个紫球,问:至少取出多少个球,才能使取出的球中至少有4个球同色?

答案

首先取光了3个篮球、3个绿球,2个紫球,然后再取3个白球,3个黄球,3个红球,这样我取了17个球,再取一个球,无论怎样都可以保证有4个白球,或黄球,或红球;保证取出的球中有4个球同色,可以取出18个球即可;

答:至少取出18个球才能保证取出的球中有4个球同色.

填空题
填空题

(41)Orientation
Yellowstone is much more than hot ground and gushing steam. Located astride the Continental Divide, most of the park occupies a high plateau surrounded by mountains and drained by several rivers. Park boundaries enclose craggy peaks, alpine lakes, deep canyons, and vast forests. In 1872, Yellowstone became the world’s first national park, the result of great foresight on the part of many people about our eventual need for the solace and beauty of wild places.
(42) When to Go
More than half of the 3 million annum visitors come in July and August. In September and early October, the weather is good, the visitors few, and the wildlife abundant. In May and June, you can see newborn animals, but the weather may be cold, wet, and even snowy. Between about No-vember 1 and May 1 most park roads are closed to vehicles.
(43) Getting There
(44) How to Visit
The 142-mile (228.5-kilometer) Grand Loop Road forms a figure eight, with connecting spurs to the five entrances. On any visit, start with the geyser basins and Mammoth Hot Springs to see wildlife and thermal features (caution: both can be hazardous if approached too closely). On the second day, travel to the Grand Canyon of the Yellowstone, Hayden Valley, and Yellowstone Lake.
(45) Park Information
Park opens year-round.
[A] Road from North Entrance to Northeast Entrance open all year; most other park roads closed to cars November through April. Call headquarters for latest weather and road conditions.
[B] Facilities for Disabled Visitor centers, Madison and Fishing Bridge Campgrounds, most rest rooms, amphitheaters, numerous ranger-led activities, walks, and exhibits are wheelchair accessible. Free brochure available.
[C] On a longer stay, visit the Northern Range, or consider a boating or fishing trip on Yellowstone Lake; a backcountry excursion on foot or horse; or any of the numerous easy nature trails throughout the park.
[D] In early years, what made Yellowstone stand out was the extravaganza of geysers and hot springs. The wild landscape and the bison, elk, and bears were nice but, after all, America was still a pioneer country filled with scenic beauty and animals.
[E] By Plane
West Yellowstone Airport (WYS) at the West Entrance of Yellowstone. (This airport is open June through September.)
Cody Airport (COD) about 50 miles (81 kilometers) from the park.
[F] During the winter season, mid-December to mid-March, Yellowstone becomes a fantasy of steam and ice; facilities are limited but sufficient. Only the road between the North and Northeast Entrances stays open to cars, but snowmobiling is permitted on unplowed roads. Heated snow coaches offer tours and give cross-country skiers access to the 50 miles (80.5 kilometers ) of groomed trails.