Question

Math makes me feel so stupid.

Answer 1

Each working at a constant rate, Rachel assembles a brochure every 10 minutes and Terry assembles a brochure every 8 minutes. Which quantity is greater, the number of minutes it will take Rachel and Terry, working together, to assemble 9 brochures, or 40?

Answer 2

D=RT

So the rate for Rachel is 1/10 and Terry 1/8, right?

Both rates = 9/40

(9/40) *2 * t =9

t=20

But It says the quantities equal for the answer.

Answer 3

To calculate Rachel's rate I said 1=10 t, t=1/10...

Answer 4

Rachel assembles 4 brochures in 4*10 =40 minutes
and Terry assembles 5 brochures in how many miniutes?

Answer 5

40

Answer 6

Yes, I know those two equal then. But i need the D=RT explanation

Answer 7

What did I mathematically do wrong?

Answer 8

(9/40) *2 * t =9

that makes sense, except for the "2" . where does that come from ?

Answer 9

The number of people. The book, in another problem, says use individual rate * # workers * time = work

Answer 10

Oh but the rate is not the same

Answer 11

if both worked at the same rate, you could do that.
but if they work at different rates, you have to add up the rates
for example, if both worked at 1/10
you could do 2*1/10
but if it's 1/10 and ⅛
you have to do (1/10 + ⅛) t = 9

Answer 12

So 9 = 9/40 t

Answer 13

yes

Answer 14

t=40 thanks @phi