Answer:
80
Step-by-step explanation:
<span>So the question is 25% of what number is 21. Lets turn that into an equation: let x be the number we are looking for. We need to take 25% from it and we know that that is equal to 21. Mathematically: 25% * x= 21. Or: (25/100) * x = 21. When we multiply both sides with 100 and divide both sides by 25 we get: x=21*(100/25). And we get that x=84. </span>
To obtain an overall average of 86%, a score of 96 is required on her 4th test.
Let the required score on her fourth test = t
The required average = 86%
Initial scores : 80% + 83.5% + 84.5%
Average = ΣX/ (fx)
fx = total score obtainable = 4 × 100 = 400
ΣX = sum of scores
Average = 86%
0.86 = ((80 + 83.5 + 84.5 + t) / 400)
86 = (248 + t) / 400
400 × 0.86 = 248 + t
344 = 248 + t
344 - 248 = t
96 = t
In other to obtain an overall average of 86%, she has to score 96 in her 4th test.
Learn more : brainly.com/question/15528814
