How the Math Skills Test works
The MST is one of the three tests behind the Officer Aptitude Rating (OAR), so everyone who sits the OAR or the full ASTB-E takes it. You sit it online in the APEX system at a recruiting station, NROTC unit or Marine Corps Officer Selection Office.
Questions come as both equations and word problems: solving for a variable, time and distance, estimating simple probabilities, fractions, roots and exponents, and the angles, areas and perimeters of shapes.
The test is adaptive. A right answer usually brings a harder question and a wrong one an easier question. You cannot skip, go back or change an answer, and the test can end before the clock once it has measured you, so the number of questions differs from person to person.
No calculator is allowed. Relevant formulas are provided on screen and you are given scrap paper.
How to approach MST questions
A routine that holds up under a clock and no calculator:
- Write down what the question asks for before you calculate, in a word or two: "current speed", "x", "area of the shaded part".
- For word problems, set up one equation from the sentence that gives the relationship, then solve it on paper.
- Look at the options before working the whole thing out. Their spread often tells you how precise you need to be.
- For exponents, rewrite both sides with the same base. For roots, look for perfect squares inside.
- Check your answer against the question, not just the arithmetic: a speed of 40 mph for a rowing boat is a sign you solved for the wrong thing.
Worked example
A time and distance question: “A boat travels 24 miles downstream in 2 hours and returns upstream in 3 hours. What is the speed of the current?” The options are (A) 2 mph, (B) 4 mph, (C) 5 mph and (D) 10 mph.
Downstream the boat makes 24 ÷ 2 = 12 mph, which is its own speed plus the current. Upstream it makes 24 ÷ 3 = 8 mph, its own speed minus the current. The difference, 12 − 8 = 4, is twice the current, so the current is 2 mph, option A. Option B forgets to halve, and option D is the boat’s speed in still water.
A probability question: “A bag holds 3 red and 5 blue marbles. Two are drawn without replacement. What is the probability both are red?” The first draw is red 3 times in 8 and the second 2 times in 7, so 3/8 × 2/7 = 6/56 = 3/28.
Tips for the real MST
- Pace for about a minute a question from the start. Questions left unreached when time runs out reduce your score, more for each one.
- Do not guess at random in the last seconds. The Navy’s own advice is that random guessing as time runs out usually costs more than the penalty.
- Learn the formulas well enough to use them without looking. The sheet saves you remembering them, not working with them.
- Practise exponent and logarithm rules, which are not on a basic formula sheet: 2^5 = 32, log base 10 of 1,000 is 3, and multiplying powers of the same base adds the exponents.
- Practise mental arithmetic with fractions and decimals. Without a calculator, slow arithmetic is what eats the clock.
Practise the Math Skills Test on CogniPrep
Our MST is free. It gives you up to 30 adaptive questions in 30 minutes, four options each, with a Formulas button for areas, perimeters, right triangles, distance and probability, and no calculator. Like the real test it gets harder as you get questions right, never lets you go back, can end before the clock once it has measured you, and takes points off if time runs out with questions unreached. Your result is our estimate on the OAR’s 20 to 80 scale, not an official score, with a breakdown of the topics you missed.