To have a maximum value, your parabola would have to open downwards. So the first 2 are wrong. Since your y-intercept is positive 4, your graph would have to touch the y axis at 4. The 3rd graph is wrong since it touches the y-axis at a negative point. The correct answer would be the 4th answer choice.
Assuming that the two investments are X & Y X + Y = 6300 X = 6300 - Y (1)
9/100X + 4/100 Y = 372 (2) replacing X from (1) into (2) 9/100(6300-Y) + 4/100 Y = 372 567 - 9/100Y +4/100Y = 372 (-9+4)/100Y = 372 - 567 5/100Y = -195 Y = 100*195/5 = 3900 From (1) we can get X X = 6300 - 3900 = 2400
A number that cannot be expressed that way is irrational. For example, one third in decimal form is 0.33333333333333 (the threes go on forever). However, one third can be express as 1 divided by 3, and since 1 and 3 are both integers, one third is a rational number.