Question 150589
Area of a trapezoid is similar to a triangle, the only difference it has 2 bases. If a triangle is {{{(1/2)(h)(b)}}}, we need to add another base to calculate for the area of trapezoid -----> {{{(1/2)h(a+b)}}}
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In the problem, let "a"=upper base="x", "b"=lower base="x+10cm", and
altitude=h=20cm
Substituting in our eqn with given, A=220 sqcm},
220 =(1/2)(20)(x+x+10) = (1/2)(20)(2x+10)
cross multiply,
440=40x+200
440-200=40x
240=40x
{{{x=6cm}}} = upper base
{{{10+6=16cm}}} = lower base
In doubt? to go back to our eqn and you'll see, A=(1/2)(h)(a+b)
thank you,
Jojo