00:01
Okay, here is our problem lydia drove home from college traveling an average speed of sixty three point four miles per hour okay, so when she's going home her rate was sixty three point four and that is miles per hour and drove back to the college the following week at an average speed of sixty three point one so when she was going back her rate was sixty three point one miles per hour and that's not that big of a difference the total round trip took five hours how much time did it take lydia to drive from home back to college? okay, the round trip took five hours okay, and we know that distance equals rate times time all right, so i don't have any idea about the time but i know together it took five hours let's just pretend for a minute, let's say that when she was going home it took her let's just i mean we're just pretending let's say it took her two hours then we would know when she's going back to college it would take three hours how'd i know that? because it took five hours total so those two have to add up to five and if you know one of them all you have to do is say five minus that to get the other one okay, so that's the key word there if i know one of the times then i just subtract it from five to get the other time.
01:56
I don't know either one of them i know that the time for one of them is t and the time for the other one is five minus that and that's all i know well, i do know that this is d and this is that same day so these two are equal to each other.
02:22
All right, so let's set it up distance equals rate times time 63 .4 times t equals 63 .1 times 5 minus t and now i can solve for t.
02:41
We've got to use distributive property here so i've got 63 .4 t equals when you multiply 63 .1 times 5 you get 315 .5 and 63 .1 times negative t is minus 63 .1 hold on.
03:13
Let me get this right here.
03:22
It's 63 .1 times t that's a t.
03:29
I was thinking i was writing my parentheses, but i've already done that so 63 .1 t...