Question

19．八年級（二）班選出部分同學(xué)參加夏令營，分成紅藍(lán)兩隊(duì)，紅隊(duì)戴紅帽子，藍(lán)隊(duì)戴藍(lán)帽子，一個(gè)紅隊(duì)隊(duì)員說：“我看見的是紅隊(duì)人數(shù)與藍(lán)隊(duì)人數(shù)相等．”一個(gè)藍(lán)隊(duì)隊(duì)員說：“我看見的紅隊(duì)人數(shù)是藍(lán)隊(duì)人數(shù)的二倍．”設(shè)紅隊(duì)、藍(lán)隊(duì)各x、y人，根據(jù)題意得（　�。�

• A． $\left\{\begin{array}{l}{x=y}\\{x=2y}\end{array}\right.$
• B． $\left\{\begin{array}{l}{x-1=y}\\{x=2y}\end{array}\right.$
• C． $\left\{\begin{array}{l}{x=y}\\{x=2（y-1）}\end{array}\right.$
• D． $\left\{\begin{array}{l}{x-1=y}\\{x=2（y-1）}\end{array}\right.$

Answer 1

分析 利用紅隊(duì)隊(duì)員看見的是紅隊(duì)人數(shù)與藍(lán)隊(duì)人數(shù)相等，可得紅隊(duì)人數(shù)-1=藍(lán)隊(duì)人數(shù)；再利用藍(lán)隊(duì)隊(duì)員說，我看見的是紅隊(duì)人數(shù)是藍(lán)隊(duì)人數(shù)的2倍，可得紅隊(duì)人數(shù)=2（藍(lán)隊(duì)人數(shù)-1）；即可得出方程組求出答案．

解答 解：設(shè)紅隊(duì)、藍(lán)隊(duì)各x、y人，依題意有
$\left\{\begin{array}{l}{x-1=y}\\{x=2（y-1）}\end{array}\right.$．
故選：D．

點(diǎn)評 此題考查了由實(shí)際問題抽象出二元一次方程組，找出題目蘊(yùn)含的數(shù)量關(guān)系是解決問題的關(guān)鍵．