In a class there are 400 students. 250 of them studying Mathematics, 150 of them studying English, 100 of them studying Biology, 100 of them studying both Mathematics and English, 60 of them studying both Mathematics and Biology, 40 of them studying both English and Biology, 30 of them studying all Mathematics, English and Biology. Find a) The number of students who are studying only Mathematics.
b) The number of students who are studying only English.
c) The number of students who are studying only Biology.
d) The number of students who are studying none of Mathematics, English and Biology.​

Martha has a deck of cards. she has lost some of the cards, and now the deck only contains nine spades, eleven diamonds, eight clubs, and twelve hearts. martha predicts that whenever she draws a card from the deck without looking, she will draw a club one-fifth of the time. which activity would best allow martha to test her prediction? a. randomly draw a card from the box and see if it is a club. b. randomly draw a card. then, continue to draw another card until all eight clubs are drawn. c. randomly draw and replace a card 120 times. then, observe how close to 30 times a club is drawn. d. randomly draw and replace a card 100 times. then, observe how close to 20 times a club is drawn.