через первую трубу бассейн наполняется за 20 ч. а через вторую - за 30 ч. за сколько часов наполнится бассейн через обе эти трубы?

Перевести John*s father likes to swim.So he often goes to the swimming pool.His moter likes to play tennis.They often go to the stadium.Their son John is seven.He wants to be a good sportsman.His mother teacher him to play tennis but he asks his parents to give him a bicycle.One day father comes home and says *I*ve got a present for you.Come and see*John comes up sees...*Oh it*s great! It *s a bicycle!I like it very much.Thank you,Daddy!I am so glad to have it.*Every day father and John go to the sports ground to ride a bike.One day John says *I can ride a bicycle very well.Let*s ask mother to go with us*So they go to the sports ground and watch John riding a bike.He rides and rides.He is happy.He says *Look,mam!No,hands!*Then he says,*Look,Dad!No feet!*The parents are very happy.Their son ride a bicycle well.But suddenly John cries *Look mam!No teeth!

в классе 30 учеников из них 17 мальчики.выразите дробью часть класса которую составляют девочки

Расшифруйте запись: ССВ : АВ = АВ. Одинаковые буквы - это одинаковые цифры, разные буквы - разные цифры. Известно, что А + В = 6. Чему равно значение разности В - С