2 years ago

Five pencils and 4 erasers cost $7.65. Four pencils and 5 erasers cost $7.20.What is the cost of 2 erasers?

1 answer:

8 0

I think this is right.. I tried my best. If u get it sorry... I’m very sorry

1. Divide 7.20 by 4 since the 4 are the pencils

2.divide 7.20 by 5 ( 5 represents the erasers )

3. Then finally multiply 1.44 from 7.20/5 and
2 and u get 2.88

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Let r3 have the euclidean inner product. let u = (-1, 1, 1) and v = (-7, 6, 15). if ||ku + v||= 7, what is k? give the exact ans

amm1812

Ma $k\mathbf u+\mathbf v=k(-1,1,1)+(-7,6,15)=(-k-7,k+6,k+15)$

Recall that for a vector $\mathbf x\in\mathbb R^n$ , we have $\|\mathbf x\|=\sqrt{\mathbf x\cdot\mathbf x}$ . So we have

$\|k\mathbf u+\mathbf v\|=\sqrt{(k\mathbf u+\mathbf v)(k\mathbf u+\mathbf v)}=7$
$\implies k^2\mathbf u\cdot\mathbf u+2k\mathbf u\cdot\mathbf v+\mathbf v\cdot\mathbf v=49$
$\implies3k^2+56k+261=0$
$\implies k=-9,-\dfrac{29}3$