Sum to n terms the series 7 +77 +777

Step-by-step explanation:

=7 (1+11+111+1111n)

=7/9 (9+99+999+9999n)

=7/9 ((10-1)+(10^2-1)+(10^3-1)+n)

=7/9 ((10+10^2+10^3...n)-(1+1+1+1n))

=7/9 ((10 (10^n-1)/(10-1))-n)

b. 1.25 hr

step-by-step explanation:

if you have a constant speed of 60 mph, then you have a ratio between 60 mi. to 1 hr. dividing both sides by 60 we get the ratio

1 mi. to

then mult. both sides by 75 we get the ratio

75 mi. to

simplifying we get

75 mi. to

or 1.25 hr.