Answer:
Step-by-step explanation:
I find it easiest to solve these using the variable to represent the number of the most-expensive item. Let x represent the number of 33-cent stamps. Then the total value (in cents) is ...
33x +24(30 -x) = 891
9x = 171 . . . . . . . . . . . . . subtract 24(30), collect terms
x = 19 . . . . . . . . . . . . divide by 9
30-x = 11 . . . . . . . find the number of 24-cent stamps
Mr. Akika had 11 24-cent stamps and 19 33-cent stamps.
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<em>Additional comment</em>
You seem to have several of these to solve. They all have a similar solution.
If we let x represent the number of higher-value items, N, the total number of items, V the total value, and v1 and v2 the individual values (v2 > v1), the equation is ...
v2(x) +v1(N -x) = V
x(v2 -v1) = V -v1·N
x = (V -v1·N)/(v2 -v1) . . . . generic solution
Using this formula in the problem here, we find ...
x = (891 -24(30))/(33 -24) = 171/9 = 19 . . . as above
