20u，silver 8u，red 3u，gold 9u，对应的mobey是$2x8u，$1x3u，$3x9u，total 46u $920，所以1u=$20，silver 个数就是8×20=160
At a recent funfair,a total of $920 was received from the sales of coloured balloons. Each silver ballon cost $2,each red balloon cost $1 and each gold balloon cost$3. Given that the 2/5 of the balloons are silver, 1/4 the remaining balloons are red and the rest are gold. How many silver balloons are sold?
Given that the 2/5 of the balloons are silver –>剩下 3/5 1 － 2/5 ＝ 3/5
1/4 the remaining balloons are red –> 剩下的要是四份 即 4的倍数 但上个条件剩下的是三份
所以 3/5 ＝ 12/20（remaining） 1/4 X 12/20 ＝ 3/20（red） 12/20 – 3/20 = 9/20 (gold) 2/5 = 8/20(silver)
然后把每8个Silver 3个red 9个gold 假想放在一组 价钱为–> $2×8=$16 $1×3=$3 $3×9=$27 $16+$3+$27=$46
$920 / $46 = 20 组 每组8个silver
20×8=160 silver balloons