Here is bob's test score math 65 arts 86 science 84 social studies 78 if his average score is 80 ,how many marks did he make in gramma
x1 = score math = 65
x2 = score arts = 86
x3 = score science = 84
x4 = score social studies = 78
x5 = score grammar
average = ( x1 + x2 + x3 + x4 + x5 ) / 5 = 80
( 65 + 86 + 84 + 78 + x5 ) / 5 = 80
( 313 + x5 ) / 5 = 80 Multiply both sides by 5
313 + x5 = 80 * 5
313 + x5 = 400 Subtract 313 to both sides
313 + x5 - 313 = 400 - 313
x5 = 87
score grammar = 87
Proof :
( x1 + x2 + x3 + x4 + x5 ) / 5 =
( 65 + 86 + 84 + 78 + 87 ) / 5 =
400 / 5 = 80