Hint
How many students study chemistry and physics, but not biology?
Answer
500 students.
Reasoning
The answer is more easily seen if three intersecting circles are drawn, and the numbers inside each section are worked out.
We know that 73 students study all three disciplines, which allows us to work out the numbers.
97 students study chemistry and physics, so 97 − 73 = 24 study just chemistry and physics.
138 students study physics and biology, so 138 − 73 = 65 study just physics and biology.
152 students study chemistry and biology, so 152 − 73 = 79 study just chemistry and biology.
280 students study chemistry, so 280 − 73 − 24 − 79 = 104 study just chemistry.
254 students study physics, so 254 − 73 − 24 − 65 = 92 study just physics.
280 students study biology, 280 − 73 − 65 − 79 = 63 study just biology.
For a total of: 104 + 92 + 63 + 24 + 65 + 79 + 73 = 500 students.
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Puzzle 268
Moving up or right, what is the largest total you can make, using the mathematical signs along the way?
+
4
−
2
+
2
2
+
2
−
2
+
−
1
+
2
−
4
2
−
1
+
1
−
+
1
−
2
+
3
3
+
3
−
4
+
Note: this puzzle is not interactive, and the numbers cannot be clicked.
