各位高手幫幫忙, 請詳解, 因為看不太懂~

grenuisx

拜託各位高手詳解, 因為小弟我數學真的不濟....
The positive square root of positive number w is multiplied by 4. If this product minus the number w equals 4, what is the value of w?

a)1
b)4
c)9
d)16
e)25


An employee is paid a salary of S dollars by the formula S=c^2-5c, where c is the number of computers she sold. How many computers must she sell in order for her to have a salary of exactly $750?

a)40
b)35
c)30
d)25
e)20

If the sum of a series of consecutive intergers from 1 to n is 190, what is the value of n?

a)11
b)15
c)19
d)23
e)27

The length of a certain rectangle is three times the width of the rectangle. If the number of the square units of its area is 16 more than the number of the linear units of its perimeter, what is the number of the square units of its area?

a)54
b)48
c)42
d)36
e)32


thanks.....

grenuisx

還有一題不知為何這樣解, 搞不懂解法.

Each team in a certain competition played exactly one game with each of the other teams. If there was a total of 28 games played in the competition, what is the number of teams in the competition

a)6     b)7     c)8       d)9      e)10

解題: T*(T-1)/2=28      為何這樣解, 搞不懂為何要.....


thanks..

grenuisx

thankssss