This is a system of equations. We can solve it by recognizing the two linear equalities we've given to solve this equation.
First, let's start off by recognizing two variables: x and y. x will be our number of hard puzzles, and y will be our number of easy puzzles. We're given that the number of hard puzzles and easy puzzles sum to 50, so we can rewrite that as:

Next, we're given that the sum of the points gained from the hard puzzles (60x), and the number of points gained from the easy puzzles (30y), sum to 1950. We can rewrite that as:

Now, we have our two linear equations, and we must solve for the hard puzzles, so x. Solving for the hard puzzles means eliminating the easy puzzles from our systems, so we can multiply our first equation by 30, and subtract it from the first equation. This is a technique called elimination.

Since x=15, Tina has solved 15 hard puzzles.
Four out of nine. There are 4 even numbers from 1-9
The position equatioin is: s(t) = –16t2<span> + </span>v0t<span> + </span>h0<span>, where </span>v<span>0 </span> represents the initial velocity of the object and h0<span> represents the initial height of the object </span>. So, since the position function represents the height of an object in t seconds, s(t)= h(t). Therefor, v0= intial velocity= 60t. Double 60t and then replace that answer with 60t from Justin's rocket's equation in order to find Pedro's rocket's equation.
Easy not to call it 2 ones and just call it 2 instead.
a tenth is 1 divided by 10 = 0.1.
20 tenths therefore is 20 times 0.1 = 2